Pediculosis and Pthiriasis (Lice Infestation) Treatment & Management
- Author: Lyn C C Guenther, MD, FRCPC, FAAD; Chief Editor: Michael Stuart Bronze, MD more...
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 7-9 days after the first treatment. For strongly ovicidal pediculicides, retreatment is recommended only if live (ie, crawling) lice are still present after treatment. Retreatment should ideally occur after all eggs have hatched but before new eggs are produced. It is extremely important to use medications as directed to ensure total eradication of the lice through their life cycle. In addition, all infested persons in a household and their infested close contacts and bedmates should be treated at the same time.
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 since the lice and eggs are killed after 5 minutes of exposure to temperatures greater than 53.5°C (128.3°F). Items that cannot be laundered can be dry-cleaned or sealed in a plastic bag for 2 weeks. 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. Children should also be educated not to share combs, brushes, hair accessories, and towels.
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. 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. 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.
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 
Centers for Disease Control and Prevention - Ectoparasitic infections. In: Sexually transmitted diseases treatment guidelines, 2010 
University of Texas, School of Nursing, Family Nurse Practitioner Program - Guidelines for the diagnosis and treatment of pediculosis capitis (head lice) in children and adults 2013 
Various topical pediculicidal agents are available for the treatment of head and pubic lice. Pyrethrin shampoos and permethrin 1% are available over the counter; permethrin 5% (approved to treat scabies, but occasionally used to treat lice), malathion 0.5% (Ovide), lindane, topical ivermectin (Sklice), and spinosad 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). Malathion lotion 0.5% is 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 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.
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.
Lindane is an organochloride that should be reserved for treatment of individuals in whom alternative treatment has failed or is intolerable.[4, 14] 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. Many authors recommend that it not be used in elderly persons or people who weigh less than 110 pounds. Because of safety concerns, retreatment should also be avoided.
Spinosad 0.9% suspension (Natroba) was approved by the FDA in 2011 for the treatment of head louse infestation in patients aged 4 years 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 soil bacteria and has ovicidal activity. Retreatment is necessary only if live (ie, crawling) lice are seen 1 week after the first treatment.
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.
Occlusive and Nonpesticide Therapy
Agents that work by clogging the respiratory spiracles of lice offer an alternative to neurotoxic pediculicides.[35, 36] This is the mechanism of action of benzyl alcohol lotion 5% (Ulesfia), which is approved by the FDA for treatment of head lice in 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.
Isopropyl myristate (Resultz) is available in Canada and Europe, but not in the United States (it is currently in phase III clinical trials). 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.
One study reported efficacy of 4% dimethicone lotion (a silicone-based lotion believed to disrupt the louse's ability to manage water) in the treatment of head lice. Another study found that 4% dimethicone lotion was a significantly more effective than malathion in most patients. NYDA is a Canadian-approved product that contains 92% dimethicone. In one study, it was found to be superior to 1% permethrin lotion. The dimethicone in NYDA replaces the air in the breathing system of lice, nymphs, and nits (eggs) and then thickens quickly, causing suffocation and death. NYDA is approved in Canada for use in individuals aged 2 years or older. This product should eliminate head lice infestations after one application; however, the product monograph recommends a second treatment to ensure complete removal of head lice.
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.
Various botanical agents have been used. Essential oils demonstrate variable efficacy and may be contact allergens. In general, the evidence supporting their efficacy is of poor quality.[39, 43] Monoterpenoids are promising agents.[39, 44, 45]
Oral anthelmintics, including ivermectin, levamisole, and albendazole,[46, 47] 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 lice. 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 of lice to the most commonly used medications for treatment of infestation (permethrin and pyrethrin) is increasing.[48, 49, 50, 51] Resistance has been reported in the United States as well as among countries in South America and Europe.
A possible mechanism of 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.[52, 53, 54, 55]
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.
Treatment of Head Louse Infestation
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. 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. 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. Nits are cemented to hair shaft and unlikely to be successfully transferred to others. 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. Commercial products include an 8% formic acid preparation (GenDerm Step 2) and an enzymatic nit remover (Clear).
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. Proper treatment with medication is advised.
Shaving is effective but is usually not necessary or socially acceptable. However, in resistant disease, it may be a consideration.
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.
Treatment of Pubic Louse Infestation
The same 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 mouse containing pyrethrins and piperonyl butoxide (RID foam).
Malathion lotion 0.5% 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.
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. Infested persons should avoid sexual contact until they have both been successfully treated. If live lice are still found, treatment should be repeated in 9-10 days. Individuals with pubic lice should also be checked for other STDs.
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. Items that cannot be laundered should be dry-cleaned or stored in a sealed plastic bag for 2 weeks.
Ophthalmic-grade petrolatum (2-4 times a day for 10 days) is often used, with good results, as an asphyxiant for eyelash infestation. 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.
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.
Treatment of Body Louse Infestation
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.
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. 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.
Treatment of Contacts
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.
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.
Deterrence and Prevention
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. 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.
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