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Lice

(Pediculosis)

By

James G. H. Dinulos

, MD, Geisel School of Medicine at Dartmouth

Reviewed/Revised Oct 2023
View PATIENT EDUCATION
Topic Resources

Lice can infect the scalp, body, pubis, and eyelashes. Head lice are transmitted by close contact; body lice are transmitted in cramped, crowded conditions; and pubic lice are transmitted by sexual contact. Symptoms, signs, diagnosis, and treatment differ by location of infestation.

Lice are wingless, blood-sucking insects that infest the head (Pediculus humanus var. capitis), body (P. humanus var. corporis), or pubis (Phthirus pubis). The 3 kinds of lice differ substantially in morphology and clinical features (see figure ). Head lice and pubic lice live directly on the host; body lice live in garments. All types occur worldwide.

Head lice

A Close-Up Look at Lice

A Close-Up Look at Lice

Head lice are most common among girls aged 5 to 11 but can affect almost anyone; infestations are less common in Black people (1 References Lice can infect the scalp, body, pubis, and eyelashes. Head lice are transmitted by close contact; body lice are transmitted in cramped, crowded conditions; and pubic lice are transmitted by... read more References ). Head lice are easily transmitted from person to person with close contact (as occurs within households and classrooms) and may be ejected from hair by static electricity or wind; transmission by these routes (or by sharing of combs, brushes, and hats) is likely but unproved. There is no association between head lice and poor hygiene or low socioeconomic status.

Infestation typically involves the hair and scalp but may involve other hair-bearing areas. Active infestation usually involves 20 lice and causes severe pruritus. Examination is most often normal but may reveal scalp excoriations and posterior cervical adenopathy.

Diagnosis of head lice depends on demonstration of living lice. Lice are detected by a thorough combing-through of wet hair from the scalp with a fine-tooth comb (teeth of comb about 0.2 mm apart); lice are usually found at the back of the head or behind the ears. Nits are more commonly seen and are ovoid, grayish white eggs fixed to the base of hair shafts. Each adult female louse lays 3 to 5 eggs/day, so nits typically vastly outnumber lice and are not a measure of severity of infestation.

Initial treatment of head lice with topical pediculicides is outlined in the table Initial Treatment Options for Lice Treatment Options for Lice Treatment Options for Lice . Medication resistance is common, and the initial choice should be based on local resistance patterns and adverse effects. Topical therapies include malathion, permethrin or other pyrethroids, spinosad, and ivermectin (2 References Lice can infect the scalp, body, pubis, and eyelashes. Head lice are transmitted by close contact; body lice are transmitted in cramped, crowded conditions; and pubic lice are transmitted by... read more References ). Lindane shampoo is no longer recommended because of the widespread resistance and risk of neurotoxicity (3 References Lice can infect the scalp, body, pubis, and eyelashes. Head lice are transmitted by close contact; body lice are transmitted in cramped, crowded conditions; and pubic lice are transmitted by... read more References ). Oral ivermectin is typically reserved for refractory infestations (4 References Lice can infect the scalp, body, pubis, and eyelashes. Head lice are transmitted by close contact; body lice are transmitted in cramped, crowded conditions; and pubic lice are transmitted by... read more References ).

After applying a topical pediculicide, nits are removed by using a fine-tooth comb on wet hair (wet combing). Termination or removal of live (viable) nits is important in preventing reinfestation; live nits fluoresce on illumination with a Wood lamp Wood Light Diagnostic tests are indicated when the cause of a skin lesion or disease is not obvious from history and physical examination alone. These include Patch testing Biopsy Scrapings Examination... read more Wood Light . Most pediculicides also kill nits. Dead nits remain after successful treatment and do not signify active infection; they do not have to be removed. Nits grow away from the scalp with time; the absence of nits less than one fourth of an inch from the scalp rules out current active infection. Hot air has been shown to kill > 88% of nits but has been variably effective in killing hatched lice. Thirty minutes of hot air, slightly cooler than a blow dryer, may be an effective adjunctive measure to treat head lice.

Controversy surrounds the need to clean the personal items of people with lice or nits and the need to exclude children with head lice or nits from school; there are no conclusive data supporting either approach. However, some experts recommend replacement of personal items or thorough cleaning, followed by drying at 54° C (130° F) for 30 minutes. Items that cannot be washed may be placed in airtight plastic bags for 2 weeks to kill the lice, which live only about 10 days.

Body lice

Body lice cause pruritus; signs are small red puncta caused by bites, usually associated with linear scratch marks, urticaria, or superficial bacterial infection. These findings are especially common on the shoulders, buttocks, and abdomen. Nits may be present on body hairs.

Diagnosis of body lice is by demonstration of lice and nits in clothing, especially at the seams.

Primary treatment of body lice is thorough cleaning (eg, cleaning, followed by drying at 65° C [149° F]) or replacement of clothing and bedding, which is often difficult because affected people often have few resources and little control over their environment (5 References Lice can infect the scalp, body, pubis, and eyelashes. Head lice are transmitted by close contact; body lice are transmitted in cramped, crowded conditions; and pubic lice are transmitted by... read more References ).

Pubic lice

Pubic lice (“crabs”) are sexually transmitted in adolescents and adults and may be transmitted to children by close parental contact. They may also be transmitted by fomites (eg, towels, bedding, clothing). They most commonly infest pubic and perianal hairs but may spread to thighs, trunk, and facial hair (beard, mustache, and eyelashes).

Images of Pubic Lice

Pubic lice cause pruritus. Physical signs are few, but some patients have excoriations and regional lymphadenopathy and/or lymphadenitis. Pale, bluish gray skin macules (maculae ceruleae) on the trunk, buttocks, and thighs are caused by anticoagulant activity of louse saliva while feeding; they are unusual but characteristic of infestation. Eyelash infestation manifests as eye itching, burning, and irritation.

Diagnosis of pubic lice is by demonstration of nits, lice, or both by close inspection (Wood lamp) or microscopic analysis. A supporting sign of infestation is scattering of dark brown specks (louse excreta) on skin or undergarments.

Treatment of pubic lice is outlined in the . Initial treatment is typically with topical pediculicides. Oral ivermectin is sometimes used for patients with pubic lice infestation that is refractory to topical therapies. Treatment of eyelid and eyelash infestation is often difficult and involves use of petrolatum, physostigmine ointment, oral ivermectin, or physical removal of lice with forceps. Sex partners should also be treated.

Table

References

  • 1. Meinking TL, Burkhart CG, Burkhart CN: Head lice. N Engl J Med347(17):1381-1382, 2002; author reply 1381-2. doi: 10.1056/NEJM200210243471720

  • 2.Nolt D, Moore S, Yan AC, et al: Head lice. Pediatrics150(4):e2022059282, https://doi.org/10.1542/peds.2022-059282

  • 3. Nolan K, Kamrath J, Levitt J: Lindane toxicity: A comprehensive review of the medical literature. Pediatr Dermatol.29(2):141-146, 2012. doi: 10.1111/j.1525-1470.2011.01519.x

  • 4. Chosidow O, Giraudeau B, Cottrell J, et al: Oral ivermectin versus malathion lotion for difficult-to-treat head lice. N Engl J Med362(10):896-905, 2010. doi: 10.1056/NEJMoa0905471. Erratum in: N Engl J Med 362(17):1647, 2010. PMID: 20220184.

  • 5. Nyers ES, Elston DM: What's eating you? Human body lice (Pediculus humanus corporis). Cutis 105(3):118-120, 2020. PMID: 32352435

Key Points

  • Head and pubic lice live on people, whereas body lice live in garments.

  • Confirm the diagnosis of lice by finding live lice or live nits.

  • Treat head or pubic lice with a topical medication (eg, a pyrethroid) or, when refractory to topical therapy, with oral ivermectin.

  • Treat body lice symptomatically and by eliminating the source of lice.

Drugs Mentioned In This Article

Drug Name Select Trade
Ovide
Acticin, Elimite, Nix Lice Killing Creme Rinse
Natroba
Sklice, Soolantra, Stromectol
G B H , GBH, Lindane
Antilirium
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NOTE: This is the Professional Version. CONSUMERS: View Consumer Version
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