Alopecia Areata

Alopecia areata is a recurrent nonscarring type of hair loss that can affect any hair-bearing area. Clinically, alopecia areata can manifest many different patterns. Although medically benign, alopecia areata can cause tremendous emotional and psychosocial distress in affected patients and their families.

The exact pathophysiology of alopecia areata remains unknown. The most widely accepted hypothesis is that alopecia areata is a T-cell–mediated autoimmune condition that is most likely to occur in genetically predisposed individuals.[8]

Autoimmunity

Much evidence supports the hypothesis that alopecia areata is an autoimmune condition. The process appears to be T-cell mediated, but antibodies directed to hair follicle structures also have been found with increased frequency in alopecia areata patients compared with control subjects. Using immunofluorescence, antibodies to anagen-phase hair follicles were found in as many as 90% of patients with alopecia areata compared with less than 37% of control subjects. The autoantibody response is heterogeneous and targets multiple structures of the anagen-phase hair follicle. The outer root sheath is the structure targeted most frequently, followed by the inner root sheath, the matrix, and the hair shaft. Whether these antibodies play a direct role in the pathogenesis or whether they are an epiphenomenon is not known.

Histologically, lesional biopsy findings of alopecia areata show a perifollicular lymphocytic infiltrate around anagen-phase hair follicles. The infiltrate consists mostly of T-helper cells and, to a lesser extent, T-suppressor cells. CD4+ and CD8+ lymphocytes likely play a prominent role because the depletion of these T-cell subtypes results in complete or partial regrowth of hair in the Dundee experimental bald rat (DEBR) model of alopecia areata. The animals subsequently lose hair again once the T-cell population is replete. The fact that not all animals experience complete regrowth suggests that other mechanisms likely are involved. Total numbers of circulating T lymphocytes have been reported at both decreased and normal levels.

Studies in humans also reinforce the hypothesis of autoimmunity. Studies have shown that hair regrows when affected scalp is transplanted onto SCID (severe combined immunodeficiency) mice that are devoid of immune cells. Autologous T lymphocytes isolated from an affected scalp were cultured with hair follicle homogenates and autologous antigen-presenting cells. Following initial regrowth, injection of the T lymphocytes into the grafts resulted in loss of regrown hairs. Injections of autologous T lymphocytes that were not cultured with follicle homogenates did not trigger hair loss.

A similar experiment on nude (congenitally athymic) mice failed to trigger hair loss in regrown patches of alopecia areata after serum from affected patients was injected intravenously into the mice. However, the same study showed that mice injected with alopecia areata serum showed an increased deposition of immunoglobulin and complement in hair follicles of both grafted and nongrafted skin compared with mice injected with control serum, which showed no deposition.

In addition, research has shown that alopecia areata can be induced using transfer of grafts from alopecia areata–affected mice onto normal mice. Transfer of grafts from normal mice to alopecia areata–affected mice similarly resulted in hair loss in the grafts.

Clinical evidence favoring autoimmunity suggests that alopecia areata is associated with other autoimmune conditions, the most significant of which are thyroid diseases and vitiligo (see History). For instance, in a retrospective cross-sectional review of 2115 patients with alopecia areata who presented to academic medical centers in Boston over an 11-year period, comorbid autoimmune diagnoses included thyroid disease (14.6%), diabetes mellitus (11.1%), inflammatory bowel disease (6.3%), systemic lupus erythematosus (4.3%), rheumatoid arthritis(3.9%), and psoriasis and psoriatic arthritis (2.0%). Other comorbid conditions found included atopy (allergic rhinitis, asthma, and/or eczema; 38.2%), contact dermatitis and other eczema (35.9%), mental health problems (depression or anxiety; 25.5%), hyperlipidemia (24.5%), hypertension (21.9%), and GERD (17.3%).[9, 10]

In conclusion, the beneficial effect of T-cell subtype depletion on hair growth, the detection of autoantibodies, the ability to transfer alopecia areata from affected animals to nonaffected animals, and the induction of remission by grafting affected areas onto immunosuppressed animals are evidence in favor of an autoimmune phenomenon. Certain factors within the hair follicles, and possibly in the surrounding milieu, trigger an autoimmune reaction. Some evidence suggests a melanocytic target within the hair follicle. Adding or subtracting immunologic factors profoundly modifies the outcome of hair growth.

Genetics

Many factors favor a genetic predisposition for alopecia areata. The frequency of positive family history for alopecia areata in affected patients has been estimated to be 10-20% compared with 1.7% in control subjects.[8] The incidence is higher in patients with more severe disease (16-18%) compared with patients with localized alopecia areata (7-13%). Reports of alopecia areata occurring in twins also are of interest. No correlation has been found between the degree of involvement of alopecia areata and the type of alopecia areata seen in relatives.

Several genes have been studied and a large amount of research has focused on human leukocyte antigen. Two studies demonstrated that human leukocyte antigen DQ3 (DQB1*03) was found in more than 80% of patients with alopecia areata, which suggests that it can be a marker for general susceptibility to alopecia areata. The studies also found that human leukocyte antigen DQ7 (DQB1*0301) and human leukocyte antigen DR4 (DRB1*0401) were present significantly more in patients with alopecia totalis and alopecia universalis.[11, 12, 13]

Another gene of interest is the interleukin 1 receptor antagonist gene, which may correlate with disease severity. Finally, the high association of Down syndrome with alopecia areata suggests involvement of a gene located on chromosome 21.

In summary, genetic factors likely play an important role in determining susceptibility and disease severity. Alopecia areata is likely to be the result of polygenic defects rather than a single gene defect. The role of environmental factors in initiating or triggering the condition is yet to be determined.

Cytokines

Interleukin 1 and tumor necrosis factor were shown to be potent inhibitors of hair growth in vitro. Subsequent microscopic examination of these cultured hair follicles showed morphologic changes similar to those seen in alopecia areata.

Innervation and vasculature

Another area of interest concerns the modification of perifollicular nerves. The fact that patients with alopecia areata occasionally report itching or pain on affected areas raises the possibility of alterations in the peripheral nervous system. Circulating levels of the neuropeptide calcitonin gene-related peptide (CGRP) were decreased in 3 patients with alopecia areata compared with control subjects. CGRP has multiple effects on the immune system, including chemotaxis and inhibition of Langerhans cell antigen presentation and inhibition of mitogen-stimulated T-lymphocyte proliferation.

CGRP also increases vasodilatation and endothelial proliferation. Similar findings were reported in another study, in which decreased cutaneous levels of substance P and of CGRP but not of vasoactive intestinal polypeptide were found in scalp biopsy specimens. The study also noted a lower basal blood flow and greater vasodilatation following intradermal CGRP injection in patients with alopecia areata compared with control subjects. More studies are needed to shed light on the significance of these findings.

Viral etiology

Other hypotheses have been proposed to explain the pathophysiology of alopecia areata, but more evidence is needed to support them. Alopecia areata was believed to possibly have an infectious origin, but no microbial agent has been isolated consistently in patients. Many efforts have been made to isolate cytomegalovirus, but most studies have been negative.[14]

The true cause of alopecia areata remains unknown. The exact role of possible factors needs to be clarified (see Pathophysiology).

No known risk factors exist for alopecia areata, except a positive family history.

The exact role of stressful events remains unclear, but they most likely trigger a condition already present in susceptible individuals, rather than acting as the true primary cause.

Frequency

Prevalence in the general population is 0.1-0.2%. The lifetime risk of developing alopecia areata is estimated to be 1.7%. Alopecia areata is responsible for 0.7-3% of patients seen by dermatologists.[15, 16]

Race

All races are affected equally by alopecia areata; no increase in prevalence has been found in a particular ethnic group.

Sex

Data concerning the sex ratio for alopecia areata vary slightly in the literature. In one study including 736 patients, a male-to-female ratio of 1:1 was reported.[17] In another study on a smaller number of patients, a slight female preponderance was seen.

Age

Alopecia areata can occur at any age from birth to the late decades of life. Congenital cases have been reported. Peak incidence appears to occur from age 15-29 years. As many as 44% of people with alopecia areata have onset at younger than 20 years. Onset in patients older than 40 years is seen in less than 30% of patients with alopecia areata.[#IntroductionMortalityMorbidity]

Alopecia areata is a benign condition and most patients are asymptomatic; however, it can cause emotional and psychosocial distress in affected individuals. Self-consciousness concerning personal appearance can become important. Openly addressing these issues with patients is important in helping them cope with the condition.

The natural history of alopecia areata is unpredictable. Most patients have only a few focal areas of alopecia, and spontaneous regrowth usually occurs within 1 year. Estimates indicate less than 10% of patients experience extensive alopecia and less than 1% have alopecia universalis. Patients with extensive long-standing conditions are less likely to experience significant long-lasting regrowth.

Adverse prognostic factors include nail abnormalities, atopy, onset at a young age, and severe forms of alopecia areata.

Patient education is a key factor in alopecia areata. Inform patients of the chronic relapsing nature of alopecia areata. Reassure patients that the condition is benign and does not threaten their general health.

Most patients try to find an explanation about why this is happening to them. Reassure these patients that they have done nothing wrong and that it is not their fault.

Inform patients that expectations regarding therapy should be realistic.

Support groups are available in many cities; it is strongly recommended that patients be urged to contact the National Alopecia Areata Foundation at 710 C St, Suite 11, San Rafael, CA 94901 or view the Web site.

Many patients are reluctant to use hairpieces or take part in support groups because, at first, these often are perceived as last-resort options. Take the time to discuss the options with patients because they are of great benefit.

The natural history of alopecia areata is unpredictable. Extreme variations in duration and extent of the disease occur from patient to patient. Alopecia areata most often is asymptomatic, but some patients (14%) experience a burning sensation or pruritus in the affected area. The condition usually is localized when it first appears. Of patients with alopecia areata, 80% have only a single patch, 12.5% have 2 patches, and 7.7% have multiple patches. No correlation exists between the number of patches at onset and subsequent severity. Alopecia areata most often affects the scalp (66.8-95%); however, it can affect any hair-bearing area. The beard is affected in 28% (males; see first image below), eyebrows in 3.8%, and extremities in 1.3% of patients (see second image below). More than one area can be affected at once.

Localized alopecia areata

Episodes of localized (< 50% involvement) patchy alopecia areata usually are self-limited; spontaneous regrowth occurs in most patients within a few months, with or without treatment.

Extensive alopecia areata

Extensive (>50% involvement) forms of alopecia areata are less common. Alopecia totalis or alopecia universalis are reported to occur at some point in 7% of patients; alopecia areata involving more than 40% hair loss is seen in 11%. The proportion of patients with alopecia totalis appears to decrease with every decade of life.

In 30% of patients with alopecia totalis, complete hair loss occurred within 6 months after onset of disease. Sharma et al[18] reported a mean progression period to alopecia totalis of 4 months after onset. The natural evolution of alopecia totalis is unpredictable, but recurrences of alopecia areata (not necessarily alopecia totalis) are expected.

In a study involving 736 patients,[17] the relapse rate was 90% over 5 years. One percent of children and 10% of adults can experience long-lasting regrowth. Forty-four percent of children and 34% of adults experience a significant period of normal or near-normal hair growth. Twenty-two percent of children and 34% of adults do not experience regrowth.

Associated conditions

Because some of the entities associated with alopecia areata occur uncommonly in the general population, a large number of patients with alopecia areata need to be examined to confirm whether an increased prevalence of these conditions exists among patients with alopecia areata. Unfortunately, most studies are performed on small groups; therefore, the data should be interpreted carefully.

Atopic dermatitis is seen in 9-26% of patients with alopecia areata. In the general population, the prevalence of atopic dermatitis in children in temperate developed countries varies from 5-20%. In adults, the prevalence decreases to 2-10%. Some authors have found atopy to be a poor prognostic factor for alopecia areata.

Vitiligo is seen with an incidence varying from 1.8-3% compared with 0.3% in control subjects. Also see Vitiligo.

Clinically evident thyroid disease was found in 0.85% of 1700 patients with alopecia areata.[19] The prevalence of thyroid disease determined on a clinical or laboratory basis varies among studies from 0.85-14.7%. The incidence of thyroid disease in control subjects is estimated to be 0.17-2%. The presence of microsomal antibodies is found in 3.3-16% of patients. Antibodies can be found with or without signs or symptoms of thyroid disease, but patients with positive autoantibodies have a higher incidence of functional abnormalities found on thyroid-releasing hormone tests (26% vs 2.8%). The incidence of thyroid microsomal and thyroglobulin antibodies in control subjects is 7%. Other studies have not supported these results. A study in 100 patients with alopecia areata failed to find an increased incidence of circulating autoantibodies, including mitochondrial and thyroglobulin antibodies.

Collagen-vascular diseases have been found in 0.6-2% of patients with alopecia areata, while the incidence in control subjects is 0.17%. The incidence of alopecia areata in 39 patients with lupus erythematous was 10% in a study by Werth et al,[20] in contrast to 0.42% of general dermatologic patients.

Diabetes mellitus was found to be more common in control subjects (1.4%) than in patients with alopecia areata (0.4%).[21] The occurrence of alopecia areata may protect against the appearance of type I diabetes mellitus. However, the incidence of type I diabetes mellitus was significantly higher in relatives of patients with alopecia areata compared with the general population.

Alopecia areata is seen in 6-8.8% of patients with Down syndrome, but only 0.1% of patients with alopecia areata have Down syndrome. The high frequency of alopecia areata in patients with Down syndrome suggests that a genetic linkage for alopecia areata may exist on chromosome 21.

Anxiety, personality disorders, depression, and paranoid disorders are seen with increased prevalence varying from 17-22% of patients, and the lifetime prevalence of psychiatric disorders is estimated to be 74% in patients with alopecia areata. Psychiatric problems are seen in both children and adults. No association has been made between the severity of the psychiatric disorder and that of alopecia areata.

Stressful life events within the 6-month period preceding episodes of alopecia areata were significantly higher in patients with alopecia areata compared with patients with androgenetic alopecia or tinea capitis.[22] Major stress factors (eg, death in family) were reported in 12% of patients.

Others associations in some studies include pernicious anemia, myasthenia gravis, ulcerative colitis, lichen planus, and Candida endocrinopathy syndrome.

Precipitating factors

A precipitating factor can be found in 15.1% of patients with alopecia areata. Major life events, febrile illnesses, drugs, pregnancy, trauma, and many other events have been reported, but no clear conclusions can be drawn. Despite these findings, most patients with alopecia areata do not report a triggering factor preceding episodes of hair loss.

The presence of smooth, slightly erythematous (peach color) or normal-colored alopecic patches is characteristic. The presence of exclamation point hairs (ie, hairs tapered near proximal end) is pathognomonic but is not always found. A positive result from the pull test at the periphery of a plaque usually indicates that the disease is active, and further hair loss can be expected. Additionally, hair loss on other hair-bearing areas also favors the diagnosis. The most common presentation is the appearance of one or many round-to-oval denuded patches. No epidermal changes are associated with the hair loss.

Alopecia areata can be classified according to its pattern. Hair loss most often is localized and patchy (see image below).

A reticular pattern occurs when hair loss is more extensive and the patches coalesce. An ophiasis pattern occurs when the hair loss is localized to the sides and lower back of the scalp (see image below).

Conversely, sisaipho (ophiasis spelled backwards) pattern occurs when hair loss spares the sides and back of the head (see image below).

Alopecia totalis occurs with 100% hair loss on the scalp (see image below).

Alopecia universalis occurs with complete loss of hair on all hair-bearing areas. Alopecia areata usually is focal; however, it can be diffuse, thereby mimicking telogen effluvium (TE) or the type of androgenetic alopecia seen in women (see image below).

See also Androgenetic Alopecia and Telogen Effluvium.

Dermoscopy

The application of dermoscopy to the evaluation of hair loss is only recently being pioneered. Dermoscopy is safe and simple, and may have great potential in the care of alopecia. However, it's diagnostic accuracy will need to be validated by well-designed studies.[23]

The presence of yellow dots seems to be a specific feature of alopecia areata and has been reported to be present in 95% of patients, regardless of their disease stages. Following histopathological correlation, these yellow dots represent degenerated follicular keratinocytes and sebum contained within the ostium of hair follicles. Although occasionally seen in advanced male-pattern hair loss, yellow dots are not seen in cases of female-pattern hair loss, scaring alopecia, or telogen effluvium.

Other dermoscopic signs reported include black dots, tapering hairs, broken hairs, and clustered short vellus hairs.

Nail involvement

Nail involvement is found in 6.8-49.4% of patients and most commonly is seen in patients with severe forms of alopecia areata. Pitting is the most common finding. Several other abnormalities have been reported (eg, trachyonychia, Beau lines, onychorrhexis, onychomadesis, koilonychia, leukonychia, red lunulae). Fingernails predominantly are affected.

Diagnosis usually can be made on clinical grounds; a scalp biopsy seldom is needed, but it can be helpful when the clinical diagnosis is less certain.

A histologic diagnosis of alopecia areata can be made when characteristic features are present. Horizontal sections usually are preferred to vertical sections because they allow examination of multiple hair follicles at different levels.

The most characteristic feature is a peribulbar lymphocytic infiltrate, which is described as appearing similar to a swarm of bees. The infiltrate often is sparse and usually involves only a few of the affected hairs in a biopsy specimen. Occasionally, no inflammation is found, which can result in diagnostic difficulties. A significant decrease in terminal hairs is associated with an increase in vellus hairs, with a ratio of 1.1:1 (normal is 7:1). Other helpful findings include pigment incontinence or the presence of eosinophils in the follicular stellae, multiple catagen hairs, hyperkeratosis of the infundibulum, and pigment casts in the infundibulum.

A shift occurs in the anagen-to-telogen ratio, which is not specific. The normal ratio is approximately 90% anagen phase to 10% telogen phase hair follicles; in alopecia areata, 73% of hairs are found to be in the anagen phase and 27% in the telogen phase. In long-standing cases of alopecia areata, the percentage of telogen-phase hairs can approach 100%. Degenerative changes of the hair matrix can be found but are uncommon.

See the treatment algorithm below.

Treatment is not mandatory because the condition is benign, and spontaneous remissions and recurrences are common. Treatments used are believed to stimulate hair growth, but no evidence indicates they can influence the ultimate natural course of alopecia areata. Treatment modalities usually are considered first according to the extent of hair loss and the patient's age.

Assessment of the efficacy of a treatment must be considered with care because the condition is highly unpredictable in presentation, evolution, and response to treatment. Little data exist regarding the natural evolution of the condition. For example, in patients with less than 40% scalp involvement, a study showed no benefit with treatment (minoxidil 1% and topical immunotherapy) over placebo.[24] The high spontaneous remission rate makes clearly assessing the true efficacy of a therapy difficult unless appropriate controls with placebo treatment are studied.

For patients with extensive alopecia areata (>40% hair loss), little data exist on the natural evolution. The rate of spontaneous remission appears to be less than in patients with less than 40% involvement. Vestey and Savin[25] reviewed 50 patients with extensive alopecia areata. Of the 50 patients, 24% experienced spontaneous complete or nearly complete regrowth at some stage during the observation period of 3-3.5 years. The relapse rate is high in patients with severe forms of alopecia areata.

Patients with alopecia totalis or alopecia universalis usually have a poorer prognosis, and treatment failure is seen in most patients with any therapy.

Because alopecia areata is believed to be an autoimmune condition, different immunomodulators have been used to treat this condition. Additional treatment options for alopecia areata include minoxidil and other treatment modalities.

Corticosteroids

Corticosteroid therapies can include intralesional injections or topical application.

Intralesional steroids

For intralesional steroids, few studies are available regarding efficacy; however, they are used widely in the treatment of alopecia areata. Intralesional steroids are the first-line treatment in localized conditions and are usually superior to topical corticosteroids.[26]

In a study including 84 patients, regrowth on treated areas was present in 92% of patients with patchy alopecia areata and 61% of patients with alopecia totalis. Regrowth persisted 3 months after treatment in 71% of patients with patchy alopecia areata and 28% of patients with alopecia totalis. Regrowth usually is seen within 4-6 weeks in responsive patients. Patients with rapidly progressive, extensive, or long-standing alopecia areata tend to respond poorly.

Another study showed regrowth in most patients (480) treated with intralesional steroids, except in two patients with alopecia universalis.

Hair growth may persist for 6-9 months after a single injection. Injections are administered subcutaneously or intradermally using a 3-mL syringe and a 30-gauge needle.

Triamcinolone acetonide (Kenalog) is used most commonly; concentrations vary from 2.5-10 mg/mL. The lowest concentration is used on the face. A 2015 study showed no difference in regrowth when using 2.5 mg/mL, 5 mg/mL, or 10 mg/mL and all were superior to placebo. A 2020 study that included 543 patients showed that 5- and 10-mg/mL concentrations may be a little more effective than concentrations of less than 5 mg/mL (< 5 mg/mL = 65%, 5 mg/mL = 80%, and 10 mg/mL = 76% of regrowth).[27] Although all concentrations were well tolerated, more cases of reversible skin atrophy were seen in the 10-mg/ml group.[28] The lowest concentration should always be used on the face to avoid skin atrophy. Caution should be used in patients with glaucoma when treating the eyebrows. It may be best to consult with their ophthalmologists.

Less than 0.1 mL is injected per site, and injections are spread out to cover the affected areas (approximately 1 cm between injection sites; see image below).

Adverse effects mostly include pain during injection and minimal transient atrophy (10%). The presence of atrophy should prompt a reduction in the triamcinolone acetonide concentration and avoidance of the atrophic site.

Injections are administered every 4-6 weeks.

Although intralesional injections of triamcinolone acetonide are usually recommended for alopecia areata with less than 50% involvement, a report showed that 6 of 10 patients with extensive alopecia areata had regrowth following injections.[29] Although injections may work in extensive alopecia areata, results are unlikely if no response is observed at 6 months (personal observation).

Topical steroids

For topical steroids, again, few studies have been performed regarding efficacy in the treatment of alopecia areata; they can however be useful, especially in children who cannot tolerate injections.

Fluocinolone acetonide cream 0.2% (Synalar HP) twice per day induced a satisfactory-to-excellent response in 61% of patients, which was maintained in 71% of patients. Children younger than 10 years responded better, as did patients with a duration of hair loss of less than 1 year.

Betamethasone dipropionate cream 0.05% (Diprosone) showed similar efficacy.

A 2005 study by Tosti et al[30] in patients with alopecia totalis or alopecia universalis showed that the use of 2.5 g of clobetasol propionate under occlusion with a plastic film 6 d/wk for 6 months induced regrowth in 8 (28.5%) of 28 patients. Regrowth was seen 6-14 weeks after the onset of therapy. Regrowth was maintained for at least 6 months after cessation of therapy in 5 (62.5%) of 8 patients. Even though only 17.8% of patients showed long-term benefits from that treatment, it should be kept in mind that the study was performed in a subgroup of patients that is usually refractory to treatment.

Treatment must be continued for a minimum of 3 months before regrowth can be expected, and maintenance therapy often is necessary.

Despite these data, the authors do not believe that monotherapy with a topical steroid has been of great benefit in the authors' practice.

The most common adverse effect is local folliculitis, which appears after a few weeks of treatment. Telangiectases and local atrophy also have been reported. No systemic adverse effects have been reported.

Immunotherapy

Topical immunotherapy[4] is defined as the induction and periodic elicitation of an allergic contact dermatitis by topical application of potent contact allergens.

Commonly used agents for immunotherapy include squaric acid dibutylester (SADBE) and diphencyprone (DPCP).[5] These 2 sensitizers are not present in the natural or industrial environment. These are compounded investigational agents not approved by the US Food and Drug Administration for use in alopecia. Dinitrochlorobenzene (DNCB) has become less popular as a result of reports that it is mutagenic in the Ames assay (a bacterial assay).

No rigorous toxicologic and pharmacologic studies have been performed on the use of these agents in humans.

Although DPCP and SADBE have not been found mutagenic in the Ames assay, neither is approved by the US Food and Drug Administration, and unknowns still exist concerning their safety profiles.

No contaminants have been found in SADBE. Acetone solutions and alcohol solutions of SADBE are equally stable for 2 months under storage conditions.

DPCP occasionally can contain mutagenic contaminants; therefore, it should be screened periodically to ensure purity. No formal data are available on DPCP regarding its longevity in solution.

Cosmetically acceptable regrowth with topical immunotherapy rates in patients with severe alopecia areata (>50% involvement) varies from 22-68%. Most studies have a success rate of 30-50%. Wiseman et al[31] retrospectively reported the results of a large cohort of 148 consecutive patients treated with DPCP.

Their analysis showed that the cumulative patient response at 32 months was 77.9%. The response rate varied with the extent of the alopecia. Cosmetically acceptable regrowth was seen in 17.4% of patients with alopecia totalis or alopecia universalis, 60.3% in patients with 75-99% hair loss, 88.1% in patients with 50-74% hair loss, and 100% regrowth in those with 25-49% hair loss.

Age at onset was also a significant variable, with older age at onset leading to a better prognosis. A lag period of 3 months was usually present between the onset of therapy and the presence of regrowth.

The median time to achieve significant regrowth was 12.2 months. Some patients showed regrowth on the treated side after 18 months of therapy. No benefit is achieved with continuing therapy after 24 months in the absence of regrowth. The relapse rate after reaching significant regrowth was 62.6%.

In a report of a 5-year experience with the use of DPCP, 97 subjects received continued therapy with DPCP. A response rate of greater than 75% was seen in 15% at 6 months, 49% at 12 months, 53% at 18 months, and 56% at 24 months. The only variable that seemed to affect response to treatment was the baseline extent of the alopecia areata. A greater than 75% response rate was seen in 100% of patients with 25-49% hair loss at baseline, 77% of those with 50-74% loss at baseline, 54% of those with 75-99% loss at baseline, 50% of alopecia totalis patients, and 41% of alopecia universalis patients demonstrated a response. Maintenance treatment (once every 1-4 wk) appeared to reduce the risk of relapse (>25% hair loss). Only 18% of patients experienced relapse on maintenance therapy, compared with 57% in those who discontinued treatment.[32]

The type of alopecia areata before treatment, duration of the disease, and the presence of nail changes were found to predict a lower response to treatment. Age at onset and sex of the patient do not appear to influence the prognosis. Controversy exists concerning whether atopy is an adverse prognosis factor.

Topical immunotherapy has been used for almost 20 years; no serious adverse effects have been reported.

The most common side effect, which is desired, is a mild contact dermatitis (redness, scaling, itching).

Adverse effects include cervical lymphadenopathy and pigment changes. Vitiligo developed on the application site in 6.7-7.5% of patients. Transient leukoderma on a distant untreated area has been reported. Of patients who develop vitiligo, 31% (4 of 13) had a history of vitiligo. Only 0.75% of patients developed hyperpigmentation. Confetti-type dyschromia (ie, hyperpigmentation, hypopigmentation) has been described as an adverse effect of DPCP treatment and occurred in 1.6% of 243 patients treated. Less common adverse effects include erythema multiforme–like eruptions and urticaria, which were reported in 3 patients treated with DPCP.

The mechanism of action of topical immunotherapy is unknown. Antigenic competition has been hypothesized. That is, the introduction of a second antigen can initiate a new infiltrate containing T-suppressor cells and suppressor macrophages that may modify the preexisting infiltrate and allow regrowth.

Because topical immunotherapy involves the production of contact sensitivity in a previously naive patient, it is best to seek approval for the treatment by the ethics review board and to have the patient sign an informed consent.

Both SADBE and DPCP appear to be equally effective. Acetone-based solutions usually are preferred because they evaporate quickly, allowing patients to wear a hat or wig immediately after treatment. Quick drying also decreases the chances of dissemination to other body parts by contact.

Treatment is provided weekly.

The patient first is sensitized directly on the scalp with a 2% concentration on a small area (2 cm).

The following week, a low concentration (0.0001%) is applied.

The concentration is increased slowly every week as needed until a mild tolerable allergic contact dermatitis is elicited. Many concentrations are available that achieve this goal.

Treating only half of the head allows the physician to use the untreated half as a control. Once regrowth occurs on the treated half, treatment can be applied to the entire scalp. If regrowth initially occurs on both sides, spontaneous remission is likely, although treatment cannot be excluded as the cause.

Avoid severe contact dermatitis. Patients are advised to avoid light exposure on the scalp for 48 hours because light degrades the chemical. Patients also are advised not to wash the scalp for 48 hours.

Initial regrowth may be seen at weeks 12-24. Once cosmetically acceptable regrowth is achieved, the treatment can be tapered gradually. Almost all patients relapse if the treatment is discontinued, and maintenance treatment is needed.

Anthralin

The efficacy of anthralin was assessed in 3 studies, which unfortunately were uncontrolled.

Both short-contact and overnight treatments have been used. Anthralin concentrations varied from 0.2-1%.

A 2004 study by Tang et al[33] showed no benefit in using anthralin. Other studies showed a response rate of 20-75%, respectively, for patchy alopecia areata and a 25% response rate for alopecia totalis. The mean time to response was 11 weeks, and the mean time to cosmetic response was 23 weeks. Anthralin was used by Tang et al in balding C3H/HeJ mice, which is one animal model for alopecia areata. Half the body was treated with anthralin 0.2%, while the other side was treated with the vehicle ointment. Regrowth was seen on the treated side in 64% of mice after 10 weeks. Four mice had almost complete regrowth. The untreated side showed either no regrowth or continued hair loss. Cytokine studies performed with an RNase protection assay showed that tumor necrosis factor-alpha and -beta were inhibited in mice that responded to treatment.

Most patients experienced irritant contact dermatitis. Whether the dermatitis is necessary for efficacy remains under debate.

Cosmetically acceptable regrowth was maintained during therapy in 71% of responders. No correlation exists between duration of the current episode and response to treatment.

Adverse effects include pruritus, erythema, scaling folliculitis, local pyoderma, and regional lymphadenopathy. Withholding treatment for a few days results in rapid disappearance of adverse effects. Treatment then can be reinstituted, but anthralin should be left on for shorter periods. Staining of clothes and skin can be a concern.

The mechanism of action of anthralin is unknown. Most likely, it creates inflammation by generating free radicals, which have antiproliferative and immunosuppressive actions.

Combination of DPCP and anthralin

A small retrospective study showed better results using both DPCP and anthralin compared with DPCP alone.[34]

Minoxidil

Minoxidil appears to be effective in the treatment of alopecia areata in patients with extensive disease (50-99% hair loss). Response rates in that group vary from 8-45%. Minoxidil was of little benefit in patients with alopecia totalis or alopecia universalis.

The 5% solution appears to be more effective.

No more than 25 drops are applied twice per day regardless of the extent of the affected area.

Initial regrowth can be seen within 12 weeks, but continued application is needed to achieve cosmetically acceptable regrowth.

Minoxidil usually is well tolerated. Adverse effects include distant hypertrichosis (5%) and irritation (7%).

The exact mechanism of action of minoxidil remains unclear. Minoxidil does not appear to have either a hormonal or an immunosuppressant effect. Minoxidil most likely has a direct mitogenic effect on epidermal cells, both in vitro and in vivo. Anagen-phase hair bulbs plucked from men applying minoxidil showed a significant increase in proliferation index as measured by DNA flow cytometry. Minoxidil also has been shown to prolong the survival time of keratinocytes in vitro. Finally, minoxidil may oppose intracellular calcium entry. Calcium influx normally enhances epidermal growth factors to inhibit hair growth. Minoxidil is converted to minoxidil sulfate, which is a potassium channel agonist and enhances potassium ion permeability, thus opposing the entry of calcium into cells. Local vasodilatation does not appear to play a primary role in hair growth associated with minoxidil.

Prostaglandin analogs

Retrospective studies using either latanoprost or bimatoprost showed some regrowth of the eyelids while using intralesional triamcinolone concomitantly on the scalp and eyebrows,[35, 36] but all prospective studies using either drugs did not show statistically significant changes when used to treat either the eyelids or eyebrows.[37, 38, 39, 40]

Psoralen plus UV-A

Many studies have been performed regarding the efficacy of psoralen plus UV-A (PUVA) in the treatment of alopecia areata, and the initial response rate varies from 20-73%. The relapse rate, unfortunately, is high (50-88%). Most patients relapse within a few months (mean 4-8 mo) after treatment is stopped.

Both systemic and topical PUVA therapies have been used.

The number of treatments required for regrowth varies, but 20-40 treatments usually are sufficient in most cases.

A younger age at onset, a longer duration of disease, and the presence of alopecia totalis or alopecia universalis appear to indicate a poorer outcome. Taylor and Hawk[41] published 10 years of experience with PUVA. The initial response rate (>90% regrowth) was comparable to other studies and was 43.8% for partial alopecia areata and 50% for alopecia totalis and alopecia universalis. However, after excluding patients with vellus hair regrowth and patients who relapsed rapidly in the follow-up period (approximately 4 mo), they found the success rate to be, at best, 6.3% for partial alopecia areata and 12.5% for alopecia totalis and alopecia universalis. They concluded that PUVA generally is not an effective long-term treatment for alopecia areata. PUVA is a relatively safe treatment modality; adverse effects include burning and, possibly, an increased risk of skin cancer. 

JAK Inhibitors

Systemic JAK inhibitors now have a significant body of data supporting their efficacy. Although results vary, it can be expected that 50% of patients will have greater than 50% regrowth. Treatment usually has to be continued to maintain efficacy.[42, 43, 44, 45, 46, 47, 48, 49, 50]  A double-blind, randomized, vehicle-controlled study showed no efficacy of ruxolitinib cream for the treatment of alopecia areata.[51]

Dupilumab has been reported as both beneficial and detrimental in cases of alopecia areata, and there is no clear conclusion at this point.[52]

Baricitinib 

Baricitinib (Olumiant) is the first systemic treatment to gain FDA approval for adults with severe alopecia areata. Baricitinib is a Janus kinase (JAK) inhibitor that blocks phosphorylation and activation of signal transducers and activators of transcription (STATs), which modulate intracellular activity including gene expression involved in the inflammatory pathway.

Approval was based on two phase 3 trials, BRAVE-AA1 and BRAVE-AA2. In BRAVE-AA1, 22% of the 184 patients who received baricitinib 2 mg and 35% of the 281 patients who received 4 mg achieved adequate scalp hair coverage, compared with 5% of the 189 patients who received placebo. In BRAVE-AA2, 17% of the 156 patients who received baricitinib 2 mg and 32% of the 234 patients who received 4 mg achieved adequate scalp hair coverage, compared with 3% of the 156 patients who received a placebo. Results were statistically significant for each treatment group compared with placebo (p < 0.001).[2]  

Ritlecitinib

Another systemic JAK inhibitor, ritlecitinib (Litfulo), has also been approved for severe alopecia areata in patients aged 12 years and older. 

Approval was based on results from the phase 2b/3 ALLEGRO study of ritlecitinib in 718 patients with alopecia areata, who had at least 50% scalp hair loss, as measured by the Severity of Alopecia Tool (SALT), including patients with alopecia totalis and alopecia universalis (complete scalp, face, and body hair loss). Statistically significantly higher proportions of patients treated with ritlecitinib had 80% or more scalp hair coverage, as measured by a SALT score of 20 or less after 6 months of treatment versus placebo. After 6 months of treatment, among those on the 50-mg dose, 23% had achieved a SALT score of 20 or less compared with 2% of those on placebo.[3]  

Safety and efficacy of ritlecitinib is continuing to be examinined in a phase 3, open-label, long-term study (ALLEGRO-LT).[53]   

Investigational Systemic Therapies

Prednisone

The use of systemic steroids for the treatment of alopecia areata is sometimes justifiable, but hair loss frequently follows discontinuation of the medication and benefits must be carefully weighed against long-term risks. Some authors support a beneficial role of systemic steroids in halting the progression of alopecia areata,[54] but many others have had poor results with this form of therapy.

The rate of regrowth varies greatly (27-89%), and many dose regimens have been used in these studies.

Although the initial regrowth appears promising, the prednisone dose necessary to maintain cosmetic growth usually must be high enough that adverse effects are inevitable, and most patients relapse after therapy is discontinued.

Some benefit was shown using minoxidil 2% solution applied twice per day following a 6-week taper of prednisone, but the relapse rate remained at a minimum of 50% at 4 months in the treated group.

Adverse effects from systemic therapy were common in these reports and included diabetes, weight gain, hypertension, psychological changes, osteoporosis, suppression of the adrenocorticotropic axes, striae, acne, hypertrichosis, and purpura.

Systemic steroids most likely are effective via their immunosuppressive effects.

An initial benefit may occur by using systemic prednisone in some patients, but the relapse rate is high, and it does not appear to alter the course of the condition.

Systemic prednisone is not an agent of choice for alopecia areata because of the adverse effects associated with both short- and long-term treatment.

Methylprednisolone administered at a dose of 500 mg/day for 3 days or 5 mg/kg twice a day over 3 days has been used in patients with widespread disease causing severe emotional distress.[55, 56] Risks and benefits of systemic steroid therapy must be weighed carefully. Predictors of response include disease duration of 6 months or less, age younger than 10 years at disease onset, and multifocal disease.

Cyclosporine

Cyclosporine has been used both topically and systemically in the treatment of alopecia areata.

Topical cyclosporine has not proven to be effective in severe alopecia areata because no patient (0 of 10) showed benefit with application of a 10% cyclosporin A (CsA) solution twice per day for 12 months.

Another study of 14 patients using a 5% solution of cyclosporine twice per day for 4-6 months reported vellus growth in 3 of 14 patients and normal hair growth in 3 patients with patchy alopecia areata. No regrowth was seen in 8 of the patients.

Neither study showed systemic absorption of CsA, and routine blood examination showed only a transient increase of hepatic enzymes in 1 patient.

Oral cyclosporine was effective in the DEBR model for alopecia areata. All rats had a full pelage by 5 weeks of treatment with 10 mg/kg/d, 5 d/wk for 7 weeks. Studies in humans also have proven efficacy with doses of 6 mg/kg/d for 3 months in 6 patients. All patients experienced regrowth, and cosmetically acceptable regrowth was seen in 3 of 6 patients. Unfortunately, all patients relapsed within 3 months of discontinuation of cyclosporine. No evidence indicates that CsA can prevent hair loss during an active episode because reports have described patients taking CsA who developed alopecia areata while they were under treatment for unrelated conditions.

The mechanism of action of cyclosporine remains unclear. It may act through its immunosuppressive effect, because, in patients who regrew hair, clearance of immune cells from the hair follicles and alteration in the balance of regulatory lymphocytes occurred (ie, decrease of the CD4/CD8 ratio). Cyclosporine causes hypertrichosis in patients treated for conditions unrelated to hair loss. The mechanism by which cyclosporine stimulates hair growth remains unknown.

In conclusion, topical cyclosporine has shown limited efficacy. Although systemic CsA appears to be effective in alopecia areata, the adverse effect profile, the recurrence rate after treatment discontinuation, and thus, the inability to produce long-term remissions, make CsA unattractive for the treatment of alopecia areata.

Tacrolimus

Regrowth was shown on the application site of topical tacrolimus in 2 studies using the DEBR model. Oral tacrolimus was ineffective. No benefit was shown in the use of topical tacrolimus for alopecia areata in a small 2005 study by Price et al that included 11 patients.[57]

Interferon

A study of 11 patients with alopecia areata ranging from patchy alopecia areata to alopecia universalis showed no benefit using intralesional interferon alfa-2 (1.5 million IU, 3 times per wk for 3 wk).

Dapsone

Dapsone at 50 mg twice per day was used in a 6-month, double-blind, placebo-controlled study. Of patients in the study, 54% (7 of 13) withdrew from the dapsone group because of adverse effects such as malaise. Of the remaining 6 patients, 3 experienced generalized growth of terminal hair, compared with 4 (4 of 13) patients in the placebo group, who experienced only sparse patchy regrowth of vellus hair. The authors concluded that although dapsone showed some efficacy, the high incidence of adverse effects rendered it unacceptable. Another study showed a rate of success comparable to the occurrence of spontaneous regrowth reported in the literature.

Methotrexate

Joly[58] reported 22 patients with long-standing, severe alopecia areata who responded well to methotrexate, with or without systemic corticosteroids. A 2016 study suggests that long-term maintenance treatment is usually required to maintain hair growth.[59] A 2019 meta-analysis including both adults and children showed that the response rate tends to be better in adults compared with children (cosmetically acceptable regrowth 70% vs 45%; complete regrowth 45% vs 12%).[60] Relapse was seen in 50% of adults and 30% of children with dose reduction or discontinuation of treatment. Adverse events, mostly increased liver enzymes, GI symptoms, and CBC count anomalies, were seen in 25% of patients. There was an average of 3 months before regrowth began, and complete regrowth could be seen after 10 months.[60] Risks versus benefits must be carefully weighed before initiating methotrexate, and the patient must be warned about the high risk of recurrence if treatment is reduced or discontinued as this is a significant source of distress.

Many other modalities have been reported to have variable response rates in small studies. These include latanoprost,[61] nitrogen mustard, massage and relaxation, isoprinosine, acupuncture, and aromatherapy, among others. The efficacy of these treatments needs to be demonstrated in larger, placebo-controlled trials before they can be recommended.

Biological agents

Data are mixed, with many prospective, randomized placebo-controlled studies[62, 63] and case reports published in the last few years regarding the use of biologic agents (including adalimumab, etanercept, and infliximab) in the treatment of alopecia areata, failing to show efficacy, and some patients developed alopecia areata while under treatment with biologic agents for other conditions.

A 2019 randomized, placebo-controlled study that included 30 patients with greater than 50% involvement showed no benefit from these drugs for the treatment of alopecia areata.[64]

Systemic JAK inhibitors now have a significant body of data supporting their efficacy. Although results vary, it can be expected that 50% of patients will have greater than 50% regrowth. Treatment usually has to be continued to maintain efficacy.[42, 43, 44, 45, 46, 47, 48, 49, 50] A double-blind, randomized, vehicle-controlled study showed no efficacy of ruxolitinib cream for the treatment of alopecia areata.[51]

Dupilumab has been reported as both beneficial and detrimental in cases of alopecia areata, and there is no clear conclusion at this point.[52]

Oral alitretinoin shows some promise.[65]

Simvastatin/ezetimibe

A prospective, open-label pilot study using simvastatin/ezetimibe showed some response that seemed to be maintained while taking the drug, but most relapsed once it was discontinued.[66] Only 19 of 29 patients completed the study. One patient was noncompliant, but reasons for lost to follow-up or withdrawal are not specified for the other patients. A 2019 retrospective study of 25 patients showed that 6 patients had a moderate or complete response to treatment, but 63% relapsed while still under treatment.[67]

Platelet-rich plasma (PRP)

PRP has both proliferation-inducing as well as anti-inflammatory effects. A small randomized, double-blind, active-controlled study showed similar efficacy between PRP and intralesional corticosteroids (26 vs 29 patients out of 40 having significant regrowth).[68]

Stem cell therapy

Mesoderm-derived stem cells are promising as a potential treatment option.[69]

Zinc

One study showed a correlation between low serum zinc levels and disease severity, as well as duration and resistance to therapies,[70] and a few reports show some benefit to using zinc gluconate (30-50 mg/day) in the treatment of alopecia areata.[71, 72] However, another study did not find a statistically significant difference in zinc concentration in serum and hair between alopecia areata patients and controls.[73]

Nonpharmacologic methods

A systematic MEDLINE search could not find any study with sufficient validity to provide scientific evidence of benefit with complementary and alternative medicine therapies for alopecia areata.[74]

A study on hypnosis for refractory alopecia areata did not show efficacy of regrowth, but it did show that hypnosis can improve depression, anxiety, and quality of life in affected patients.[75]

Cosmetic treatments for patients with alopecia areata include dermatography and hairpieces. Dermatography has been used to camouflage the eyebrows of patients with alopecia areata. Follow-up visits at 4 years showed that 30 of 39 of patients demonstrated excellent cosmetic results and 3 had good results. On average, 2-3 sessions lasting 1 hour each were required for each patient. No adverse effects were reported. Hairpieces are useful for patients with extensive disease and allow them to carry on their usual social life. Reassure patients about the natural look provided by hairpieces.

Surgical intervention has no role in the treatment of alopecia areata.

Alopecia areata is highly unpredictable. No treatment is effective in preventing or halting progression of the condition. No trigger can be found to explain disease exacerbation in most patients.

The first systemic immunotherapy, baricitinib (Olumiant), was approved by the FDA in June 2022 for adults with severe alopecia areata.[2]  Therapies commonly prescribed include corticosteroid injections, corticosteroid creams, minoxidil, anthralin, topical immunotherapy, and phototherapy. The choice of one agent over the others depends on patient age (children do not always tolerate adverse effects), extent of condition (localized vs extensive), and the patient's personal preference. The University of California (San Francisco) and University of British Columbia have devised a treatment algorithm that can guide the physician in the treatment of alopecia areata (see image below). 

For patients younger than 10 years, options include corticosteroid creams, minoxidil, and anthralin. For adults with less than 50% scalp involvement, the first option usually is an intralesional corticosteroid, followed by corticosteroid cream, minoxidil, and anthralin. For adults with greater than 50% scalp involvement, topical immunotherapy and phototherapy are additional options.

Class Summary

Glucocorticoids have anti-inflammatory properties and cause profound and varied metabolic effects. In addition, these agents modify the body's immune response to diverse stimuli.

Topical corticosteroids (including intralesional corticosteroids) are safe and easy to use. They are acceptable cosmetically and allow patients to wear hats or wigs shortly after application. They also are relatively inexpensive. While the usefulness of high-potency topical corticosteroids is under debate, they remain a good (painless) option in children.

Intralesional steroids are first-line treatment in localized conditions.

Oral prednisone usually is reserved for patients with rapidly progressive alopecia areata. The relapse rate is high, and the potential for multiple severe adverse effects when used long term limits its usefulness.

Clobetasol propionate (Temovate)

Clobetasol propionate is a class I superpotent topical steroid. It suppresses mitosis and increases the synthesis of proteins that decrease inflammation and cause vasoconstriction. Treatment should continue until cosmetically acceptable regrowth is achieved or for a minimum of 3-4 months.

Prednisone (Deltasone, Meticorten, Sterapred)

Prednisone is an immunosuppressant occasionally used in rapidly progressive alopecia areata in an attempt to halt the condition, but the relapse rate is high. Use of systemic steroids for the treatment of alopecia areata is under much debate. Prednisone stabilizes lysosomal membranes and suppresses lymphocytes and antibody production.

Many drug doses and regimens have been used in the treatment of alopecia areata, but no formal recommendation exists.

Triamcinolone (Kenalog 10 mg/mL or 40 mg/mL)

In alopecia areata, intralesional triamcinolone is believed to suppress the immune system locally and thereby allow hair to regrow. Injections are administered with 3-mL syringe and 30-gauge needle intralesionally.

Pediatric patients generally are less tolerant of intralesional injections because of local discomfort.

Betamethasone dipropionate cream 0.05% (Diprosone)

Betamethasone dipropionate is used for inflammatory dermatoses responsive to steroids. It decreases inflammation by suppressing the migration of polymorphonuclear leukocytes and reversing capillary permeability.

Class Summary

Vasodilators relax arteriolar smooth muscle, causing vasodilation; hair growth effects are secondary to vasodilation.

Minoxidil topical (Rogaine Extra Strength)

Minoxidil stimulates hair growth in general and is effective in many types of hair loss. The exact mechanism of action remains unclear, but it does not appear to have either hormonal or immunosuppressant effects. The 5% solution appears to be more effective.

Class Summary

These agents inhibit Janus kinase 3 (JAK3) and the tyrosine kinase expressed in hepatocellular carcinoma (TEC) kinase family by blocking adenosine triphosphate (ATP) binding site. 

Baricitinib (Olumiant)

Indicated for adults with severe alopecia areata.

Ritlecitinib (Litfulo)

Indicated for patients aged 12 years and older with severe alopecia areata. 

Class Summary

Because alopecia areata is believed to be an autoimmune condition, different immunomodulators have been used to treat the condition. Exact mechanism of action of topical immunotherapy is unknown. Antigenic competition was hypothesized (ie, introduction of a second antigen can initiate a new infiltrate containing T-suppressor cells and suppressor macrophages that may modify preexisting infiltrate and allow regrowth).

Commonly used agents for immunotherapy include SADBE and DPCP. These are compounded investigational agents not approved by the US Food and Drug Administration for use in alopecia.

Cyclosporine (Sandimmune, Neoral)

Cyclosporine is used both topically and systemically for the treatment of alopecia areata. Topical cyclosporine has shown limited efficacy. Although systemic CsA appears to be effective in alopecia areata, the adverse effect profile, recurrence rate after treatment discontinuation, and inability to produce long-term remissions make CsA unattractive for the treatment of alopecia areata. The mechanism by which cyclosporine stimulates hair growth remains unknown. It may act through its immunosuppressive effect because patients who regrew hair had clearance of immune cells from the hair follicles and alteration in the balance of regulatory lymphocytes (ie, decreased CD4/CD8 ratio). Cyclosporine causes hypertrichosis in patients treated for conditions unrelated to hair loss.

Methoxsalen (8-MOP, Oxsoralen)

Methoxsalen inhibits mitosis by binding covalently to pyrimidine bases in DNA when photoactivated by UV-A.

Anthralin (Dritho-Scalp 0.5% cream, Anthra-Derm 1% cream, Drithocreme 1%, Micanol 1% cream)

Anthralin is a synthetic derivative of a tree bark extract. Its mechanism of action in alopecia areata is unknown. Most likely, it creates inflammation by generating free radicals, which have antiproliferative and immunosuppressive actions. Both short-contact and overnight treatments have been used. High concentration (1-3%) is used for short-contact treatments. Lower concentrations (0.1-0.4%) are used for overnight treatments. Applications in excessive amounts may stain clothing.