Pubic Lice

🧭 When to suspect

Pubic lice (Phthirus pubis, colloquially "crabs") are tiny, crab-shaped insects around 2 mm long that live on coarse body hair and feed on blood. They spread almost entirely by close body contact – most often sexual contact – and only rarely through shared bedding, towels or clothing; condoms do not prevent transmission, and infestation is unrelated to hygiene. Because they share a route of transmission with other genital infections, a diagnosis of pubic lice is a marker of sexual risk and should trigger a full sexual health assessment.

The cardinal symptom is itch in the affected area, typically worse at night, which may take up to 3 weeks to develop after exposure (occasionally there is prolonged, asymptomatic carriage). Patients may have noticed the lice or eggs (nits) attached to hair shafts, blue macules (maculae caeruleae) on the lower abdomen or thighs, dark rust-coloured specks of louse faeces in the underwear, or specks of blood from scratching. Lice favour coarse hair and may also involve the axillae, trunk, thighs, beard, moustache, eyebrows and eyelashes – but not the scalp, whose fine hair they cannot grip.

The primary-care tasks are simple but easily skipped: confirm the diagnosis by seeing a louse or nit (itch alone is not enough); treat the patient, partners and environment together; screen for coexisting sexually transmitted infections (STIs); and, in any child, consider safeguarding.

Source: BASHH · NHS