“Crabs” is the common name for a pubic lice infestation, caused by tiny parasitic insects called Phthirus pubis that live in coarse body hair, most often in the pubic area. Despite the name, it’s not technically a disease but rather an ectoparasitic infestation, meaning the insects live on the outside of your body and feed on your blood. Crabs spread primarily through sexual contact and cause intense itching, but they’re treatable with over-the-counter products.
What Pubic Lice Are
Pubic lice are a distinct species from head lice. They’re extremely small, roughly 1.1 to 1.8 millimeters long, and have a broad, flat body with large front claws that make them look like miniature crabs under magnification. Those crab-like claws are specifically adapted to grip coarse hair, which is why they settle in the pubic region, though they can also appear in armpit hair, chest hair, beards, and even eyelashes.
The lice go through three life stages: egg, nymph, and adult. Females glue their eggs (called nits) to the base of hair shafts, and these hatch after about a week. The nymphs molt three times over the next one to two weeks before reaching adulthood. An adult female lays roughly 30 eggs over her 3- to 4-week lifespan. Adults are entirely dependent on human blood and will die within 24 to 48 hours if they’re removed from a host.
How Crabs Spread
The most common route of transmission is direct body contact during sex. Because the lice crawl rather than jump or fly, they need close, sustained contact to move from one person to another. Occasionally, pubic lice can spread through shared clothing, bedding, or towels. Transmission from a toilet seat is theoretically possible but extremely rare, since lice can’t survive long away from a human body and their claws aren’t designed to grip smooth surfaces.
Having crabs doesn’t mean you’re unclean. Lice are equal-opportunity parasites that will infest anyone whose body provides the right type of hair and a blood supply. However, because they spread through intimate contact, a diagnosis often prompts screening for other sexually transmitted infections as a precaution.
Symptoms to Look For
The hallmark symptom is itching in the pubic area, which usually begins about five days after infestation but can take longer. The itch comes from an allergic reaction to louse saliva injected during feeding. It tends to be worse at night, when the lice are most active.
Beyond itching, you may notice:
- Nits on hair shafts. These look like tiny, oval, yellowish-white dots firmly attached near the base of the hair. They don’t flake off like dandruff.
- Visible lice. With careful inspection you can sometimes see the adult lice clinging to hairs, though they’re small enough to be easy to miss.
- Bluish-gray spots on the skin. Called maculae ceruleae, these small discolorations appear at feeding sites and are a distinctive sign of pubic lice.
- Dark specks in underwear. These are louse droppings, which look like tiny rust-colored or black dots.
Persistent scratching can break the skin and lead to secondary bacterial infections, causing redness, swelling, or crusting in the affected area. If you notice signs of infection beyond the normal itch, that warrants attention from a healthcare provider.
How Crabs Are Treated
Most cases clear up with over-the-counter lice-killing products. The standard options are lotions or cream rinses containing permethrin (1%) or a mousse containing pyrethrins with piperonyl butoxide. You apply the product to all affected hairy areas, leave it on for the time specified on the label (typically about 10 minutes), and then rinse it off.
A single treatment often isn’t enough. You should check for live lice after about 9 to 10 days, and if any are still present, repeat the treatment. Eggs can survive the first round, so the second application catches newly hatched nymphs before they mature and start laying eggs of their own.
If over-the-counter products don’t work, prescription alternatives are available. These include a stronger topical lotion that’s left on for 8 to 12 hours, or an oral medication that paralyzes and kills the lice from the inside. The oral option also requires a repeat dose 7 to 14 days later, since it doesn’t kill eggs.
When Lice Reach the Eyelashes
In rare cases, pubic lice infest the eyelashes, a condition sometimes seen in children who contract lice through close household contact. Standard lice-killing lotions can’t be applied near the eyes. Instead, treatment typically involves applying petroleum jelly (like Vaseline) to the lashes several times a day to suffocate the lice by blocking their breathing holes. A doctor may also physically remove lice and nits with fine forceps. In some cases, an oral medication is used alongside these methods.
Cleaning Your Environment
Treating your body alone isn’t enough if lice or eggs are lurking in your bedding or clothing. On the day you begin treatment, wash all bed linens, towels, and recently worn clothing in hot water and dry them on the hottest dryer setting. Items that can’t be machine-washed can be sealed in a plastic bag for two weeks, which is long enough for any surviving lice or hatching nymphs to die without a blood meal.
You don’t need to fumigate your home or spray furniture. Pubic lice can’t survive more than 48 hours away from a human body, so a standard cleaning routine for soft surfaces is sufficient. Focus your effort on fabrics that had direct contact with your body in the days before treatment.
Preventing Reinfestation
Any sexual partners from the past month should be notified and treated at the same time, even if they aren’t showing symptoms yet. If only one partner is treated, the lice will simply pass back and forth. Avoid sexual contact until both you and your partner have completed treatment and confirmed the infestation has cleared.
Condoms do not prevent pubic lice, since the insects live in hair rather than on genital skin. The only reliable way to avoid transmission is to avoid close body-to-body contact with someone who has an active infestation. Shaving pubic hair removes the habitat lice need, but this isn’t a practical or recommended prevention strategy on its own, since lice can colonize other coarse body hair.