What Are Crabs? Pubic Lice STD Explained
Crabs are pubic lice — tiny parasitic insects that infest coarse body hair, spreading through close contact including sex, bedding and towels. They cause intense itching (worse at night), visible tan-gray crabs about 1–2mm long, and white egg clusters glued to hair shafts. Treatment: over-the-counter 1% permethrin lotion plus hot-washing bedding; sexual partners treat simultaneously.
Meet Pthirus pubis
Pubic lice are wingless insects evolutionarily specialized for one niche: coarse human hair. Adults measure 1–2mm — barely visible tan-to-gray crabs with oversized claws gripping hair shafts. They feed on blood several times daily, staying glued to skin between meals, and survive off a human body only 1–2 days.
Despite the name, they colonize any coarse hair: pubic region, thighs, armpits, chest, beard, eyebrows — never the smooth scalp (that's head lice's territory).
How to tell if you have crabs
- Itching that intensifies at night — the feeding schedule's signature.
- Visual confirmation: look for moving specks at hair bases, or white oval nits cemented firmly to shafts (dandruff flakes off; nits don't).
- Blue-gray spots (maculae ceruleae): feeding-site marks on skin.
- Rust-colored powder in underwear: lice droppings.
- Irritation from scratching: secondary skin infection risk follows.
A magnifying glass over pubic hair after a warm shower catches them mid-crawl — diagnosis is visual, no lab required.
How crabs spread
| Route | Risk level |
|---|---|
| Sexual/skin contact — the classic STI route | Highest |
| Shared bedding, towels, clothing | Moderate — viable lice wait 1–2 days |
| Toilet seats | Near zero — feet can't grip smooth surfaces |
| Pets | None — species-specific; your dog is innocent |
Finding crabs without recent sexual contact usually points to shared bedding — though discovering them in teens warrants an honest conversation about sexual activity, since intimate contact dominates transmission in that age group.
Getting rid of them for good
- Permethrin 1% cream rinse (OTC) — apply to affected hairy areas, wait 10 minutes, rinse. Repeat in 7–9 days to hatchlings.
- Alternative: pyrethrin with piperonyl butoxide; prescription ivermectin or malathion for resistant cases.
- Launder everything: bedding, towels, recent-worn clothes — machine wash hot (130°F+) and dry high heat, or seal unwashables in plastic for 2 weeks.
- Treat partners simultaneously; pause sexual contact until cleared.
- Eyebrow/eyelash cases: see a clinician — never apply OTC products near eyes.
The bonus screening rule: crabs travel with company. Diagnosis should trigger full STI paneling — studies find co-infection rates substantial enough that guidelines recommend it routinely (panel guide).
Frequently asked questions
Sources & further reading
- 📚 CDC — Pubic lice ('crabs') — www.cdc.gov/pubic-lice/about
- 📚 CDC — Clinical guidance: pediculosis — www.cdc.gov/std/treatment-guidelines/pubic-lice.htm
- 📚 MedlinePlus — Pubic lice — medlineplus.gov/pubiclice.html