Pediculosis
Lice infestation of head (capitis), body (corporis), or pubic area (pubis); intense itch and visible lice or nits.
Also known as: lice, pediculosis capitis, pediculosis corporis, pediculosis pubis, head lice, crabs
Overview
Cutaneous infestation by parasitic blood-feeding lice. Three species infect humans: Pediculus humanus capitis (head louse), P. humanus corporis (body louse), and Pthirus pubis (pubic/crab louse).
Epidemiology
Head lice affect 6-12 million US children annually, ages 3-11 most common, female > male. Body lice are a disease of poverty, homelessness, displacement, and war — vector for Bartonella quintana, Rickettsia prowazekii (epidemic typhus), Borrelia recurrentis. Pubic lice are sexually transmitted in adults; incidence declining with grooming practices.
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Risk factors
- Head lice: school-age children, shared brushes/hats/helmets, sleepovers
- Body lice: homelessness, poor hygiene, crowded conditions, refugee settings
- Pubic lice: sexual activity (high turnover), other STIs
- Long hair (slight risk increase for head lice)
Pathophysiology
Lice feed on human blood every 4-6 hours and cannot survive >24-48 hours off the host. Females lay eggs (nits) cemented to hair shafts close to scalp/skin; nits hatch in 7-10 days; adults mature in another 7-10 days and live 30 days. Itching is delayed hypersensitivity to louse saliva injected during feeding.
Clinical presentation
Symptoms
- Intense pruritus of scalp (capitis), trunk (corporis), or pubic area (pubis)
- Sleep disturbance, irritability in children
- Posterior cervical or occipital lymphadenopathy (head lice)
Signs / physical exam
- Head lice: live lice on scalp (best seen behind ears and at nape); nits — oval yellow-white 0.5-1 mm — firmly attached to hair shaft within 6 mm of scalp; viable nits closer to scalp, dead/hatched nits further out; excoriations and impetigo from scratching
- Body lice: lice and nits in seams of clothing (not on body); excoriations, papules, hyperpigmentation, lichenification on shoulders, trunk, waistline ('vagabond's disease')
- Pubic lice: lice and nits attached to pubic hairs; may infest eyelashes (especially in children — pediatric phthiriasis palpebrarum is a sentinel for sexual abuse), eyebrows, axillae, beard, perianal hair; maculae ceruleae — bluish macules at feeding sites
Classic findings
Live louse or viable nit close to scalp = active infestation; nits >6 mm from scalp may be dead/hatched (not necessarily active).
Differential diagnosis
- Seborrheic dermatitis / dandruff (vs nits) — Scale moves freely; nits are firmly attached to hair shaft and slide along it only with effort
- Hair casts / hair sleeves — White cylindrical concretions slide easily; no lice
- Scabies — Burrows in web spaces; not localized to scalp
- Eczema / contact dermatitis — No live lice or nits on inspection
- Tinea capitis — Patchy alopecia with scale and broken hairs; KOH positive
- Folliculitis — Pustules around hair follicles; no lice
Diagnostic workup
Diagnostic criteria
Visualization of live louse or viable nit confirms infestation.
Labs
- Clinical diagnosis by direct visualization of live lice or viable nits
- Wet-comb method (lice comb through wet conditioned hair) is most sensitive
- Dermoscopy or microscopy to confirm nits and viability
- Pubic lice → screen for other STIs (gonorrhea, chlamydia, syphilis, HIV)
- Body lice → consider screening for Bartonella, typhus, relapsing fever in appropriate epidemiologic settings
Imaging
- Not indicated
Diagnostic algorithm
| Variant | Site | First-Line Therapy |
|---|---|---|
| Pediculosis capitis | Scalp — nits within 6 mm of scalp | Permethrin 1% or pyrethrin (repeat day 7-10); resistance → ivermectin 0.5% / spinosad / malathion; wet combing |
| Pediculosis corporis | Lice in clothing seams; trunk/waist papules | Improve hygiene, launder clothing at 149°F; pediculicide rarely needed |
| Pediculosis pubis | Pubic/perianal/axillary/beard hair; eyelashes (children = abuse red flag) | Permethrin 1%; eyelashes → petrolatum BID × 8 d; STI screen + treat contacts |
Treatment
First-line
- Head lice: topical pediculicide — permethrin 1% lotion or pyrethrin/piperonyl butoxide shampoo (OTC); apply 10 min, rinse; REPEAT in 7-10 days; in areas with documented resistance, use first-line alternative — topical ivermectin 0.5% lotion (single application, no nit combing required), spinosad 0.9% topical suspension, or malathion 0.5% lotion
- Wet combing with fine-toothed nit comb (e.g., LiceMeister) every 3-4 days for 2 weeks — adjunct to pediculicide or stand-alone
- Decontamination: wash bedding/clothing in hot water (≥130°F) and dry on high heat; non-washable items bagged for 2 weeks (lice die in 1-2 days off host); soak combs/brushes in hot water 10 min
- Body lice: improve hygiene — bathe, change into clean clothes; launder all clothing/bedding at 149°F (65°C); pediculicide rarely needed; treat secondary bacterial infections
- Pubic lice: topical permethrin 1% or pyrethrin to affected areas; repeat in 7-10 days; treat sexual contacts; eyelash involvement — petrolatum (Vaseline) BID × 8 days to suffocate lice, manual removal of nits; physostigmine and oral ivermectin alternatives
Pediculicide-resistant or refractory
- Oral ivermectin 400 mcg/kg on day 0 and day 7 (off-label) — effective for resistant head lice
- Topical benzyl alcohol 5% lotion, spinosad 0.9%, abametapir 0.74% (newer agents)
- Wet combing every 3-4 days × 4 weeks as monotherapy
Second-line / adjunct
- Avoid lindane (neurotoxicity, FDA black box) — use only when other agents fail
- DO NOT use kerosene, gasoline, or dog/cat shampoos (toxic, ineffective)
- Schools should follow 'no nit' policies cautiously — current AAP/CDC guidance favors NOT excluding children with nits alone
Complications
- Secondary bacterial infection (impetigo, folliculitis, cellulitis) from scratching — most common complication
- Cervical/occipital lymphadenopathy
- Body lice as vectors: epidemic typhus (R. prowazekii), trench fever (B. quintana), louse-borne relapsing fever (B. recurrentis)
- Pubic lice in children — sentinel for sexual abuse (eyelash involvement)
- Sleep disturbance, school absences, social stigma
- Coexisting STIs in adults with pubic lice
PANCE pearls
- Nits >6 mm from scalp are usually empty shells (dead/hatched); only viable nits within 6 mm represent active infestation.
- Persistent failure of permethrin should prompt suspicion of resistance, not noncompliance — switch agent class.
- Body lice live in clothing seams, not on the body — examine the clothes.
- Pubic lice in a child — especially eyelash involvement — is a red flag for sexual abuse; report appropriately.
- DO NOT exclude children from school for nits alone — current pediatric guidance no longer supports 'no-nit' policies.
References
- AAP 2015 — Head Lice — Clinical Report (Devore, Schutze, AAP Council on School Health and Committee on Infectious Diseases, Pediatrics 2015)
- CDC 2024 — CDC Parasites — Lice (Pediculosis) Health Professional Resources
- AAD 2020 — Diagnosis and Management of Head Lice Infestation (AAD review series)
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