To test for crabs at home, examine the coarse hair of your pubic and perianal area under good light, ideally with a magnifying lens, looking for slow-moving lice or for nits (eggs) cemented to hair shafts. Pubic lice are visible to the naked eye, so spotting an adult louse or its eggs confirms the diagnosis.
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 |
How crabs are tested and diagnosed
Pubic lice are caused by Pthirus pubis, a small insect that feeds on blood and clings to coarse body hair, mainly the pubic and perianal region, but sometimes the armpits, chest, beard, or even the eyelashes CDC. Unlike most STIs, there's no lab test, no urine cup, and no blood draw. You diagnose it by finding the bug or its eggs.
Diagnosis is made by finding a crab louse or nits on the hair in the affected area CDC DPDx. Adult lice are roughly the size and shape they're named for: broad, crab-like, and grayish-tan, turning darker after a blood meal. They move slowly and grip the base of the hair. Nits are tiny oval eggs glued firmly to the hair shaft, usually near the skin, and they don't brush off the way dandruff or lint does.
How to do the self-exam
- Use bright, direct light and a handheld magnifying lens. The lice are small, and a lens makes the difference between guessing and confirming.
- Part the coarse hair and inspect the skin at the base, where lice attach to feed and where nits are cemented to the shafts.
- Look for movement: adult lice cling tightly but shift when disturbed, while nits stay fixed in place.
- Check beyond the groin if you have symptoms elsewhere. The perianal hair, lower abdomen, thighs, chest, armpits, beard, and rarely the eyelashes and eyebrows can all be involved.
- Look for tiny bluish spots or specks of dark debris on the skin or underwear, which can accompany an infestation.
People most often mistake other hair debris for nits. If something brushes off easily, it's probably not an egg. If it's stuck fast and oval, it likely is. When you can't tell, a clinician can confirm with the same visual method, sometimes under microscopy.
When to look after a possible exposure
Crabs aren't found by a window-period blood test, so timing works differently than it does for infections like HIV or syphilis. After contact, it can take time before lice grow large enough to spot and before eggs are laid and visible. The itch that usually tips people off starts after the lice have been feeding for a while, because it's an allergic reaction to their bites rather than an instant response. If you've had a known exposure but see nothing yet, re-check over the following days, and don't assume one clean look rules it out.
If you're also worried about other infections from the same encounter, those do have testing windows worth respecting. See our guide on when to test after exposure so you screen at the right time rather than too early.
Who should check or get screened
Anyone with new itching in the pubic area, a new sexual partner, or a partner who's been diagnosed should examine themselves. Because pubic lice spread mostly through sexual contact, finding them is a reasonable prompt to screen for other STIs too. Co-infections are common, and many STIs cause no symptoms at all.
- Anyone with persistent itching, visible lice, or nits in coarse body hair.
- Recent sexual partners of someone with a confirmed infestation, even without symptoms yet.
- People with new or multiple partners, who benefit from routine STI screening regardless of crabs.
- Anyone who notices the bugs while also having symptoms of another infection, such as discharge or sores.
Getting tested: the exam, at-home kits, and cost
Because crabs are diagnosed by sight, a clinic visit is brief: a clinician looks at the area, often with a lens, and tells you on the spot, with no waiting on a lab. Most STIs are diagnosed from a simple sample, a urine cup, a self-collected swab, or a quick exam, with results usually back in a few days. At-home STI kits don't test for lice the way they test for chlamydia or gonorrhea. For crabs, the at-home step is your own careful visual exam, with a clinician confirming if you're unsure.
Cost rarely needs to be a barrier. Pubic lice care and broader STI screening are free or low-cost at health departments, Planned Parenthood, and Title X clinics. If you want to handle the rest of an STI panel privately, you can get tested with an at-home kit, and you can compare testing providers before you choose one.
Reading your results
For crabs, your result is what you see. A live louse or firmly attached nits in the hair means an active infestation, with none of the ambiguous gray zone you get with a borderline antibody titer. Empty, hatched egg casings further from the skin can linger after treatment and don't necessarily mean you still have living lice; what matters is whether you find moving adults or fresh nits close to the skin. If your exam is negative but the itching persists, get seen, because itch in this area can also come from eczema, other skin conditions, or a different STI.
If you find crabs
Crabs are treatable with a defined course, usually a medicated wash or cream applied to the affected hair. Read the full crabs treatment guide for how each option is used and what to expect.
Two rules make or break it: finish the entire course even once the itching eases, and treat your partner at the same time so you don't pass the lice back and forth. Decontaminate recently worn clothing and bedding too, and follow our advice on how to prevent crabs & avoid reinfestation. Clinics handle this daily, and it says nothing about you as a person.
When to see a clinician
See a clinician if you can't confirm what you're seeing, if treatment doesn't clear the lice, if the itching continues after a full course, or if lice involve the eyelashes, which need special handling and shouldn't be treated with the products used elsewhere. Get medical care promptly if scratched skin becomes red, swollen, warm, or starts oozing, which can signal a secondary bacterial skin infection. For the less common downstream problems and how to recognize them, see crabs complications.