Crabs symptoms most often show up as intense itching in the genital area, plus tiny lice or pale eggs (nits) glued to the base of coarse pubic hair. Some people also notice small bluish-gray spots on the skin where lice have fed, or sores from scratching. Many infestations cause no symptoms at all.
with the right treatment
testing, not symptoms, decides
| Item | Value |
|---|---|
| Curable? | yes — with the right treatment |
| Tested by | exam + lab |
| Often | no symptoms |
| If you may have it | get tested — testing, not symptoms, decides |
What are the symptoms of crabs?
Pubic lice (Pthirus pubis) are small blood-feeding insects that anchor in coarse body hair and bite the skin to feed CDC, Pubic Lice. The symptoms you feel come from those bites and from your body's reaction to them. Here's what each one actually is.
Itching in the genital area
The classic sign is itching around the pubic hair, perianal area, or wherever lice have settled. It's an allergic reaction to louse saliva, so it tends to build over time and is frequently worse at night, when the lice are most active. The itch can be relentless enough to disturb sleep — that's often what sends people to look closely in the first place.
Visible lice and nits
Adult crab lice are tiny, tan-to-grayish, and broad — under a hand mirror or magnifying glass they look a bit like a sea crab, which is where the nickname comes from. They cling near the skin where they feed. Nits (the eggs) are even smaller, oval, and cemented firmly to the hair shaft near the base; unlike dandruff or lint, they don't brush off. Seeing either confirms an active infestation.
Blue spots (maculae ceruleae)
A detail most overviews skip: some people develop small, slate-blue or grayish spots on the skin of the lower abdomen, thighs, or buttocks, called maculae ceruleae. They're thought to come from the louse's saliva reacting with blood pigment under the skin at the bite site. They don't hurt and fade on their own, but if you spot them alongside genital itching, they're a strong clue toward pubic lice rather than another rash.
Sores and skin irritation
Scratching breaks the skin, which can leave red marks, raw patches, or scabs. If bacteria get into those broken areas, a secondary skin infection can develop, with extra redness, warmth, or oozing. You may also notice tiny dark specks (louse droppings) or rust-colored flecks of dried blood on your underwear.
Where crabs show up — including the spots people miss
Despite the name, crab lice aren't limited to pubic hair. They prefer coarse hair, so they can spread to the perianal area, the thighs and lower abdomen, the armpits, the chest or abdominal hair, a beard or mustache, and — notably — the eyelashes and eyebrows. Eyelash involvement is more common in children and is worth a clinician's attention. The hair on the scalp is a different texture and usually isn't affected. If you find them beyond the groin, here's a guide to crabs in eyebrows, eyelashes & other body hair.
How soon do crabs symptoms appear after exposure?
There's usually a lag. After a first exposure, itching often takes one to several weeks to develop, because your skin has to become sensitized to louse saliva before the allergic itch kicks in. That means you can carry lice — and pass them on — before you feel anything. People who've had pubic lice before may react faster the next time. If you're trying to figure out timing around a recent encounter, see when to test after exposure.
What people mistake crabs for
Genital itching has a long list of causes, so crabs get confused with several of them. The way to tell the difference is to look closely for the actual lice or firmly attached nits — that's the feature other conditions don't share.
- Jock itch or other fungal rashes — these cause itching and a spreading red border but no visible insects or eggs.
- Contact dermatitis or razor irritation — itchy, bumpy skin from shaving, soaps, or fabrics, again without lice.
- Folliculitis — inflamed hair follicles that look like small pimples, sometimes mistaken for nits.
- Scabies — another itchy infestation, but caused by a microscopic mite that burrows into skin rather than a visible insect on the hair.
- Eczema or psoriasis — chronic itchy patches that don't come and go with a clear exposure.
Complications if crabs go untreated
Pubic lice aren't known to transmit other diseases, so the risks are mostly local and manageable — but they're real if you ignore them.
- Secondary bacterial skin infection — when scratching breaks the skin and bacteria move in, causing redness, warmth, swelling, or pus that may need treatment.
- Persistent, sleep-disrupting itch — ongoing irritation that wears on you and can leave the skin thickened or discolored from chronic scratching.
- Eye irritation from eyelash involvement — lice on the lashes can cause itchy, crusted, or inflamed eyelid margins (a form of blepharitis), which needs careful, eye-safe treatment rather than standard lice products.
- Ongoing transmission — untreated lice keep spreading to partners and household contacts through close contact and, less often, shared bedding or towels.
Most cases clear with over-the-counter or prescription treatment; you can read through how to get rid of crabs at home for what that involves.
Who should get screened
Pubic lice are diagnosed by finding the lice or nits, not by routine lab screening, so there's no population-wide screening program the way there is for some STIs. The practical rule: if you have unexplained genital itching, if you can see lice or nits, or if a sexual partner has been diagnosed, get checked. Because crabs spread through close sexual contact, finding them is also a reasonable prompt to talk with a clinician about testing for other infections — people who have one STI often benefit from a fuller checkup.
How crabs are diagnosed
Diagnosis is usually a quick visual exam — a clinician (or you, with good light and magnification) looks for live lice or firmly attached nits on the hair, sometimes confirmed under a microscope CDC DPDx. It's fast and doesn't require blood work. If you also want to rule out other infections, you can get tested; many of those tests are a simple urine cup or self-collected swab, with results usually back in a few days and free or low-cost at health departments, Planned Parenthood, and Title X clinics.
When to see a clinician
See a clinician if you can't tell what you're dealing with, if over-the-counter treatment doesn't clear it, if lice involve the eyelashes or a child, if you're pregnant, or if scratched skin looks infected (spreading redness, warmth, or pus). A diagnosis here is common and entirely treatable — clinics handle it daily, and it says nothing about you as a person.