Pubic lice
Exam Tips
- Diagnosis in OSCEs is clinical: finding live lice or viable nits is the decisive point.
- Dead nits may remain attached after successful treatment; persistent itch alone does not equal treatment failure.
- If live lice persist, first check application technique/adherence, then switch to the alternative insecticide.
- Always mention STI screening and partner notification when sexual transmission is likely.
- Eyelash disease is treated differently: use ophthalmic occlusive ointment in children and in pregnancy/breastfeeding.
- Image-oriented revision: identify crab-shaped louse morphology and maculae ceruleae on dermatoscopic/clinical photographs.
Definition
Pubic lice (pediculosis pubis) is an ectoparasitic infestation caused by Phthirus pubis, a human blood-feeding louse that typically inhabits pubic and perianal coarse hair. It is most commonly sexually transmitted, but can occasionally spread through close personal contact or contaminated bedding/clothing, and diagnosis is confirmed by identifying live lice or viable nits on examination.
Pathophysiology
Phthirus pubis has egg (nit), nymph, and adult stages; eggs hatch in about 6-10 days and nymphs mature over roughly 2-3 weeks. Adult lice grasp coarse hair with pincer-like claws and feed on blood, producing pruritus through a delayed hypersensitivity reaction to salivary antigens (often delayed 4-6 weeks in first infestation, then 1-2 days on re-exposure). Persistent scratching causes excoriation and may permit secondary bacterial infection; chronic inflammation can lead to lichenification and hyperpigmentation. Lice survive only briefly off the host (usually 24-48 hours), which explains why close contact is the main transmission route.
Risk Factors
- Sexual contact with an infested partner
- Multiple or new sexual partners
- Household or close body contact with an infested person
- Sharing infested towels, bedding, or clothing
- Presence of untreated sexual contacts (risk of reinfestation)
Clinical Features
Symptoms
- Genital itching, often worse at night
- Perianal itch
- Irritation in other coarse-hair areas (axillae, chest, beard, thighs)
- Ocular irritation if eyelashes are involved
Signs
- Visible crab-shaped lice (~2 mm, grey-brown/grey-white) attached to coarse hairs
- Nits (yellow-white ovoid eggs) firmly attached to hair shafts
- Maculae ceruleae (small blue-grey macules)
- Erythematous papules at feeding sites
- Rust-coloured specks on skin/underwear (louse faeces)
- Excoriations, impetigo/cellulitis, or chronic lichenification/hyperpigmentation
- Eyelash involvement with possible blepharitis/conjunctivitis signs
Investigations
Management
Lifestyle Modifications
- Explain transmission and treatment technique clearly; poor application is a common reason for failure
- Avoid sexual/close body contact until patient and partner(s) complete treatment
- Wash clothing, towels, and bedding at >=50 C; alternatively dry-clean or seal non-washables in a plastic bag for 2 weeks
- Remove remaining nits with a fine-tooth comb (dead nits can persist and do not alone indicate treatment failure)
- Arrange review about 1 week after treatment completion to check for live lice
- Refer to GUM/sexual health services for partner tracing (previous 3 months) and STI testing when sexually transmitted route is likely
- In children, consider safeguarding assessment for possible sexual abuse while recognizing non-sexual transmission can occur
Pharmacological Treatment
Topical pediculicide (first-line body-hair infestation, age >=6 months)
- Permethrin 5% cream: apply to affected coarse-hair regions (pubic/perianal, inner thighs to knees, trunk hair contiguous with pubic area, infested facial hair excluding eyelashes/eyebrows), leave 8-12 hours or overnight, then wash off; repeat after 7 days
- Malathion 0.5% aqueous solution: topical alternative regimen for non-eyelash pubic lice (use according to product directions and repeat course if required)
Permethrin 5% is licensed for crab lice in adults and children >2 months. Avoid eye contact; do not apply to broken or secondarily infected skin. Use caution in pregnancy/breastfeeding, and supervise older adults; children should use under medical advice. Adverse effects can include transient burning, paraesthesia, pruritus, erythema, dry skin; rare hypersensitivity reactions.
Eyelash infestation therapy
- Simple eye ointment BP or paraffin eye ointment: apply to eyelid margins twice daily for 8-10 days
- Permethrin 1% lotion to eyelashes with eyes closed, wash off after 10 minutes (alternative in selected adults)
For people <18 years or pregnant/breastfeeding, prefer inert occlusive ophthalmic ointment/paraffin eye ointment. Do not use regular petrolatum (e. g, Vaseline) in eyes due to irritation risk.
Complications
- Excoriation from scratching
- Secondary bacterial skin infection (e. g, impetigo, cellulitis)
- Lichenification and post-inflammatory hyperpigmentation in chronic infestation
- Blepharitis, conjunctivitis, or corneal epithelial keratitis when eyelashes are affected
- Reinfestation, especially if partners are untreated
Prognosis
Infestation usually clears with correct topical therapy plus partner/environmental control, but it rarely resolves without treatment. Reinfestation is not uncommon (reported around 7.6% in one large STI-clinic cohort), so follow-up and partner management are key.
Sources & References
💊BNF Drug References(4)
- Dimeticone[management.pharmacological]
- Malathion[management.pharmacological]
- Malathion[cautions]
- Permethrin[management.pharmacological]
✅NICE Guidelines(1)
- Pubic lice[overview]
📖Textbook References(7)
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1483)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 26)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1833)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1656)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1656)[context]
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 1483)[context]
- Oxford Handbook of Clinical Diagnosis (Huw Llewelyn, Hock Aun Ang, Keir Lewis etc.) (Z-Library).pdf(pp. 169, 170, 171)[context]