Pediculosis and Pthiriasis (Lice Infestation) Treatment & Management

Treatment of pediculosis has 2 aspects: medication and environmental control measures. Increasing emphasis is being placed on understanding the life cycle of lice in order to provide effective treatment.

Not all treatment preparations are ovicidal. For weakly ovicidal or non-ovicidal pediculicides, routine retreatment is recommended typically 7-10 days after the first treatment. For strongly ovicidal pediculicides, retreatment is recommended only if live (ie, crawling) lice are still present after treatment.  ^[28]  Retreatment should ideally occur after all eggs have hatched but before new eggs are produced. ^[4] It is extremely important to use medications as directed to ensure total eradication of the lice through their life cycle. Different head lice medications should not be used at the same time. In addition, all infested persons in a household and their infested close contacts and bedmates should be treated at the same time. If an approved treatment has been properly applied and live lice are still present, a full course of treatment of another class of age-appropriate topical medication should be used.  ^[28]  The Canadian Pediatric Society recommends pyrethrins and permethrin as first-line treatments and isopropyl myristate and dimethicone as second-line therapies in cases of treatment failure. ^[38]

Head lice have been found on hats, scarves, brushes, combs, hair accessories, linens, towels, and stuffed animals. Since exposure to these fomites could result in infestation, it is recommended that such items used by the infested person within 2 days prior to pediculicide treatment be machine washed with hot water and dried with hot air cycles since the lice and eggs are killed after 5 minutes of exposure to temperatures greater than 130°F. ^[4] Items that cannot be laundered can be dry-cleaned or sealed in a plastic bag for 2 weeks. ^[4] The floors and furniture should be vacuumed in order to remove hairs from an infested individual, which might have been shed with viable nits attached. ^[4] Children should also be educated not to share combs, brushes, hair accessories, and pillow.  ^[28]

In the treatment of body lice, medications are less essential than environmental measures. Patients with body lice should have infested clothing, bedding, and towels laundered with hot water (at least 130°F) and then dried in a dryer using a hot setting. ^[10] For items that cannot be washed in a washing machine, the CDC recommends dry-cleaning or sealing and storing for 2 weeks in a plastic bag. ^[13] If the patient maintains hygiene with regular appropriate laundering of clothing, changes into clean clothing at least weekly, and avoids the sharing of clothing, beds, bedding, and towels used by other infested individuals, pediculicides are generally not required. If hygiene cannot be maintained, treatment with a pediculicide used to treat head lice may be necessary. Fumigation or dusting with chemical insecticides is occasionally needed to control and prevent spread of louse-bourne infections. ^[10]

Related clinical guideline summaries include the following:

• British Association for Sexual Health and HIV -United Kingdom National Guideline on the Management of Phthirus pubis infestation ^[39]

• CDC: Parasites - Lice ^{[4, 10, 13]}

• American Academy of Pediatrics: Head Lice

• Canadian Pediatric Society: Head Lice

Various topical pediculicidal agents are available for the treatment of head and pubic lice. Pyrethrins with piperonyl butoxide (A-200, Pronto, R&C, Rid, Triple X), permethrin 1% lotion (NIX), dimethicone (LiceMD Pesticide Free) and mineral oil–based products (Nix Ultra shampoo) are available over the counter; malathion 0.5% (Ovide), lindane 1% shampoo and lotion, ivermectin 0.5% lotion (Sklice), spinosad 0.9% (Natroba), and benzyl alcohol 5% lotion (Ulesfia) are prescription agents.

Pubic lice can be treated with over-the-counter permethrin 1% lotion and a mousse containing pyrethrins and piperonyl butoxide (RID foam). ^[13] Lindane shampoo (1%) is FDA approved as second-line treatment of pubic lice (crabs). Dimethicone, malathion, ivermectin, spinosad, and benzyl alcohol are currently not US Food and Drug Administration (FDA) approved to treat pubic lice.

Pyrethrin and permethrin kill live lice, but not unhatched eggs. A second treatment 9-10 days after the first treatment is recommended in order to kill any newly hatched lice before they can produce new eggs. Pyrethrin is derived from chrysanthemums and is approved for use in children aged 2 years or older. It should not be used by individuals who are allergic to chrysanthemums or ragweed. Piperonyl butoxide has been added to pyrethrin products to enhance efficacy and to minimize the potential for resistance. ^[6]

Examples of pyrethrin/piperonyl butoxide combination formulations include A200 Maximum Strength, A200 Lice Control, A-200 Lice Treatment, A200 Time-Tested Formula, A200 Lice Killing Shampoo, Good Sense Lice Killing Shampoo, Step 1, Lice Treatment gel, Lice-X, Licide shampoo, Leader Lice Solution, Medi-Lice maximum strength, Pronto Plus Lice Killing shampoo, Pronto Maximum strength, Pronto Lice Kill System, Pyrinex, Pyrinyl II, Pyrinyl Liquid Shampoo, Pyrinyl Liquid, R&C Lice Treatment Kit, RID Pediculicide, RID shampoo/spray kit, RID foam, RID gel, and Tisit shampoo.

Permethrin is a synthetic pyrethroid similar to the naturally occurring pyrethrins from the chrysanthemum flower. Permethrin 1% lotion is approved for use in children aged 2 months or older.

Malathion is an organophosphate that has proven to be more ovicidal than permethrin and has a higher lethal effect and decreased frequency of re-infestation, if used properly. It is approved for use in individuals aged 6 years or older. Malathion 0.5% lotion (Ovide) is flammable and should not be used in the presence of hot hair care products or near individuals who are smoking. If lice are still present at 7-9 days, a second treatment should be given.

Lindane is an organochloride that should be reserved for treatment of individuals in whom alternative treatment has failed or is intolerable. ^{[4, 13]}  Due to its neurotoxicity, lindane is not recommended by the American Academy of Pediatrics (APP), the Centers for Disease Control and Prevention (CDC), or the Medical Letter. ^[28]  Seizures may result from abnormal absorption or gross overuse of the product. It should not be used in patients with a defective cutaneous barrier, premature infants, people with seizure disorders, or pregnant or breastfeeding women. ^[13] Many authors recommend that it not be used in elderly persons or people who weigh less than 110 pounds. ^[13] Because of safety concerns, retreatment should also be avoided.

In February 2012, topical 0.5% ivermectin (Sklice) was approved in the United States as a single-dose, 10-minute application without the need for nit combing in individuals aged 6 months or older. Although it is not ovicidal, it appears to prevent nymphs from surviving. ^[4]

Spinosad 0.9% suspension (Natroba) was approved by the FDA in 2011 for the treatment of head louse infestation in patients aged 6 months and older. The product is applied to dry hair as a cream rinse, left in for 10 minutes, and then shampooed out. Spinosad is derived from the soil bacterium Saccharopolyspora spinosa. It has ovicidal activity. Retreatment is necessary only if live (ie, crawling) lice are seen one week after the first treatment. A phase 3 study showed that spinosad was more efficacious in clearing head lice than permethrin (P< 0.001). ^[40]  

Abametapir (Xeglyze) is a topical 0.74% lotion indicated as a single 10-minute treatment for head lice in patients aged 6 months and older. It acts by inhibiting metalloproteinase, which is critical to egg development and survival of lice. Abametapir has been approved for treatment of head lice in patients 6 months and older by the FDA in 2020; however, it is not yet commercially available in the United States.  ^[28]

Two studies (n=704) showed that 81.5% of abametapir treated individuals were free of lice 2 weeks after a single application compared with 49.1% treated with vehicle (P < 0.001). ^[41] Ovicidal efficacy was measured by recording the hatch rate of eggs collected from each subject’s hair before and after treatment and incubated for 14 days. With abametapir, 100% of treated eggs remained unhatched compared with 64% for vehicle. Accounting for pretreatment hatch rates, the absolute reduction in egg hatching was 92.9% for abametapir versus 42.3% for vehicle (P < 0.0001). ^[42]  

Agents that work by clogging the respiratory spiracles of lice offer an alternative to neurotoxic pediculicides. ^{[43, 44]} This is the mechanism of action of benzyl alcohol lotion 5% (formerly known as Ulesfia), which was approved by the FDA for treatment of head lice in 2009 for patients aged 6 months or older; the benzyl alcohol inhibits lice from closing their respiratory spiracles, allowing the lotion to obstruct the spiracles. The lotion is given in 2 applications 1 week apart for 10 minutes; it needs to be applied twice because it kills only lice, not nits. Benzyl alcohol lotion may be an easier and safer alternative to lindane and malathion. Because its mechanism of action is physical rather than chemical, development of resistance should not be a concern. In clinical studies, more than 75% of those treated with benzyl alcohol lotion became lice-free. ^[45]  However, this treatment is no longer available by manufacturer and there are not indications it will be brough back in the future.  ^[28]

Isopropyl myristate (Resultz) is available in Canada and Europe and received FDA approval for treatment of head lice in 2017, although it is not yet marketed in the United States. It is a non-insecticide–based drug that contains isopropyl myristate, an ingredient commonly used in cosmetics. Its mode of action is a mechanical process that weakens the waxy shell of lice, resulting in internal fluid loss and dehydration. ^[46] It requires only a 5-minute application time.

Dimethicone is available in the United States as an over-the-counter liquid gel formulation containing 100% dimethicone (LiceMD Pesticide Free) and in Canada and Europe as NYDA dimeticone 100 cSt Solution, 50% w/w. Dimethicone replaces the air in the breathing system of lice, nymphs, and nits (eggs); thickens quickly; and then causes suffocation and death. ^[47] Dimethicone can be used in individuals aged 2 years or older. LiceMD should be applied for 10 minutes; the hair is then combed with the included lice comb while LiceMD is still in the hair. Afterward, the hair is shampooed with regular shampoo and warm water. In contrast, NYDA is left on for 8 hours. After it has been on for 30 minutes, the dead lice and eggs should be combed out using the included NYDA lice comb. The hair should not be washed for 8 hours. Although NYDA should eliminate head lice after one application, the product monograph recommends a second application after 8-10 days to ensure complete removal of head lice. A small open-label US study showed that, after 14 days following 1-3 treatments with the 100% dimethicone gel regimen, 96.5% were free of live lice and 80.7% of viable eggs. ^[48] In another study, NYDA was found to be superior to 1% permethrin lotion. ^[49]

The mineral oil–containing shampoo Nix Ultra shampoo suffocates lice. It also contains fragrance, laureth-4, MIPA laureth sulfate, and propylene glycol. It should be applied to dry hair for 10 minutes. Afterward, water is added to the hair, which is lathered and rinsed off. It is used in infested individuals aged 1 year or older and is not intended for pubic lice. ^[50]

Other occlusive therapy techniques, such as vinegar, mayonnaise, petroleum jelly, olive oil, butter, isopropyl alcohol, and water submersion as long as 6 hours, have been advocated, but most have not been scientifically evaluated. However, a dry-on, suffocation-based pediculicide (DSP) lotion was found to be effective in open trials. ^[43]

Various botanical agents have been used. Essential oils demonstrate variable efficacy and may be contact allergens. ^[51] In general, the evidence supporting their efficacy is of poor quality. ^{[52, 53]} Monoterpenoids are promising agents. ^{[52, 54, 47]}

Oral anthelmintics, including ivermectin, levamisole, and albendazole, ^{[55, 56]} have been found to be effective against head louse infestation, but are not approved by the FDA to treat lice. Oral ivermectin has also been successfully used to treat pubic and head lice, but is not FDA approved for these conditions. ^[13] Administration should be repeated in 7-10 days to kill lice emerging from nits that may have survived the first treatment. Trimethoprim-sulfamethoxazole was initially reported to be effective; however, controlled studies have shown only minimal efficacy.

Resistance

Resistance of lice to the most commonly used medications for treatment of infestation (permethrin and pyrethrin) is increasing. ^{[57, 58, 59, 60]} Resistance has been reported in the United States as well as among countries in South America and Europe.

A possible mechanism of drug resistance development includes mutations of target enzymes (eg, acetylcholinesterase) so that the enzymes no longer bind the organophosphate permethrin with the same affinity. Another possible mechanism is increasing the metabolism of the insecticides through an increase in monooxygenase enzyme activity, turning them into harmless compounds before they can cause damage. ^{[61, 62, 63, 64, 65, 66]}

Resistance to malathion has been reported in the United Kingdom; however, the UK formulation contains only malathion, whereas, in the US formulation, malathion is coupled with isopropyl alcohol and terpineol.

Medicated lotions or shampoos may be used to eliminate head lice. Empiric treatment of all contacts is not needed; only contacts with confirmed infestation should also be treated; however, prophylactic treatment of bedmates of an infested individual is prudent. ^[4] Re-treatment after 7-10 days is recommended with many agents to eradicate any lice that hatched from nits after the initial treatment. It is important to read the instructions before applying the pediculicide to ensure that the medication has been left on for the appropriate amount of time and washed off properly.

Hair conditioner and combination shampoo/conditioner products should not be used prior to pediculicide application, and the hair should not be re-washed for 1-2 days after the pediculicide is removed. ^[4] Hair conditioners may prevent binding of the pediculicides to the hair shafts. After treatment, the infested individual should put on clean clothing.

Mechanical removal and shaving

The CDC, American Association of Pediatrics, and National Association of School Nurses recommend that school “no-nit” policies be discontinued. ^[4] Nits are cemented to hair shaft and unlikely to be successfully transferred to others. ^[4] Nonetheless, some schools still have a no-nit policy. In such cases, nits can be mechanically removed with fine-tooth combs. Soaking the hair in a solution of equal parts water and white vinegar and then wrapping the wet scalp in a towel for at least 15 minutes may facilitate removal. Battery-powered combs for louse removal including MagiComb and Robi-Comb claim to kill live lice but there are no randomized-controlled studies to support these claims.  ^[28]

Most studies have shown that mechanical removal alone (ie, wet-combing every 2-3 days for a minimum of 2 weeks) is not as effective as mechanical removal combined with a pediculicide. ^[65] Proper treatment with medication is advised.

In some areas, colloquilly known "lice ladies" may offer mechanical lice removal services but these treatments are often expensive. 

Shaving is effective but is usually not necessary or socially acceptable. However, in resistant disease, it may be a consideration.

Environmental eradication

Since head lice can sometimes be spread by sharing hats, hair bands and accessories, and towels that have been in contact with an infested person’s hair, any object that the infested child or parent has come into contact with should be considered a potential fomite. It may be beneficial to launder potential fomites (eg, towels, pillowcases, sheets, hats, toys) in hot water, followed by machine drying using the hottest cycle. Temperatures exceeding 130°F (55°C) for more than 5 minutes kill eggs, nymphs, and mature lice. Items that are not machine washable may be placed in a dryer at high heat for 30 minutes. Dry cleaning may be an effective alternative.

Because adult lice cannot survive for long if separated from a host and because eggs hatch in 6-10 days and nymphs die without a blood meal, carefully sealing potential fomites in plastic bags for 2 weeks can be effective. This technique works well for objects such as stuffed animals that do not tolerate laundering or dry cleaning. Vacuuming selected areas of the home, such as couches used by infested patients, is recommended by some as an adjunctive control measure.

Combs and hair brushes can be discarded or soaked for at least 5 minutes in very hot water (>130°F [>55°C]).

Chemical insecticide sprays used in the home environment have not been shown to be effective in the control of head lice.

Providing education to children about the sharing of hats, combs, and hair-ties is also prudent. Giving children separate areas to store their belongings in the classroom may help prevent the spread of lice. ^[4]

Many of the pediculicides used for head louse infestation are also used for pubic louse infestation. In addition, P pubis infestations of the eyelashes are treated with occlusive therapies.

Pubic lice can be treated with over-the-counter permethrin 1% lotion and a mousse containing pyrethrins and piperonyl butoxide (RID foam). ^[13] Although malathion lotion 0.5% has been used to treat pubic lice, it is currently not FDA approved to treat pubic lice. Lindane shampoo causes neurotoxicity and should not be used as a first-line agent; it should be reserved for cases of resistance or when other medications are not tolerated. ^[13]

Sexual partners of a person infested with pubic lice should be informed that they are at risk for infestation and should be treated if the sexual contact occurred within a month prior to diagnosis. ^[13] Infested persons should avoid sexual contact until they have both been successfully treated. ^[13] If live lice are still found, treatment should be repeated in 9-10 days. ^[13] Individuals with pubic lice should also be checked for other STDs. ^[13]

The infested areas should be washed and towel dried. The instructions on the pediculicide should be read and carefully followed. The pubic hair and other infested areas (excluding eyebrows and eyelashes) should be thoroughly saturated with the pediculicide. After leaving on the pediculicide for the recommended time, it should be removed according to the package instructions. Clean clothing and underwear should be put on after treatment. Towels, clothing, and bedding used within the 2-3 days before treatment should be machine-washed in water of at least 130°F and dried in a hot dryer. ^[13] Items that cannot be laundered should be dry-cleaned or stored in a sealed plastic bag for 2 weeks. ^[13]

Ophthalmic-grade petrolatum (2-4 times a day for 10 days) is often used, with good results, as an asphyxiant for eyelash infestation. ^[13] The petrolatum covers the lice and their nits, preventing respiration. The dead lice are removed mechanically, usually with tweezers. Mercuric oxide ointment is also useful in the treatment of eyelash infestation with P pubis. If only a few live lice and nits are on eyelashes and/or eyebrows, it may be possible to remove them with a nit comb or fingernails. ^[13]

Fluorescein dye strips, which are used in the diagnosis of corneal abrasions, may be used in combination with white petrolatum. The strips are applied to the eyelashes for 3 nights.

Use of a pediculicide is usually unnecessary with P humanus corporis infestation because the lice live on the clothing. Treatment of clothing and bed linens includes laundering in hot water, ironing with a hot iron, or drying in a hot dryer. Dry cleaning is also effective for killing lice and their nits on clothing.

Education about hygiene and accessibility to laundering facilities are important in preventing the spread of body lice and re-infestation. ^[66]

Topical agents can be applied to clothing, especially the seams. Published data suggest that permethrin spray can help prevent body louse re-infestation.

In cases of heavy pediculosis, treatment of the body with a pediculicide shampoo or lotion may be beneficial, especially if the patient also has confirmed or suspected concomitant head or pubic louse infestation. Oral ivermectin 12 mg given as 3 doses 7 days apart has also been shown to be effective in a cohort of homeless men. ^[26] None of these agents is currently labeled or marketed for treatment of body lice in the United States. In some cultures, monkeys are used as patient nit pickers to groom the hair and to remove adult lice and nits.

The treatment of infested family members, friends, and/or other close contacts at the same time as the infested individual is important in helping to prevent further spread of head lice and in preventing re-infestation. In the case of pubic lice, all sexual partners from within the previous month should be treated. ^[13]

Patient education regarding treatment of contacts is essential. Parents with children who are infested should be advised to treat all infested family members with a pediculicide and to provide environmental fomite control.

Education about hygiene and accessibility to laundering facilities are important in preventing the spread of body lice and re-infestation. ^[66]

Causes of therapeutic failure include the following:

• Misdiagnosis
• Inappropriate treatment
• Noncompliance
• Insufficient application of pediculicide 
• Lack of ovicidal activity of pediculicide and failure to re-treat within 7-10 days 
• Lack of removal of live nits
• Lack of environmental eradication
• Sharing clothing, bedding, and towels used by a person infested with body or pubic lice 
• Failure to treat close contacts 
• Re-infestation
• Resistance to pediculicide 

To prevent head lice re-infestation, all household members and contacts of a patient should be examined and treated at the same time if infested. Bedmates should also ideally be treated even if they do not show evidence of infestation. Washing combs, brushes, and other fomites may reduce re-infestation.

Children should be educated not to exchange or use another child's hat, comb, or brush. Some parents choose to extend this prohibition to use of "common" headwear such as is available in the dress-up area of various play spaces or public libraries.

Once an infestation has been identified and treated, ongoing vigilance with close, direct visualization of hair and scalp at periodic intervals is recommended.

Sexual partners within the previous month of individuals with pubic lice should be treated at the same time as the infested individual. Sexual contact should be avoided between sexual partner(s) until they have both been successfully treated. ^[13] Bed linens, towels, and underwear and clothing should be washed at the same time as treatment with medication.

Prevention of re-infestation with body lice can be accomplished by ensuring that infested clothing, bedding, and towels were appropriately laundered with hot water (at least 130°F) and then dried in a dryer using a hot setting to destroy the lice, improving the individual’s hygiene, regularly laundering clothing, and changing to clean clothing at least weekly. ^[10]

It should be noted that social distancing and isolation may prevent the spread of lice. Studies that occurred during lockdown periods in the COVID-19 pandemic suggest decreased prevalence of head lice and a decrease in pediculicide sales during isolation times.  ^{[17, 19]   [18]}