When someone says they “have crabs,” they’re referring to an infestation of pubic lice, tiny parasitic insects that attach to coarse body hair and feed on blood. The nickname comes from the lice’s appearance under magnification: they have a round, flat body with large front claws that look remarkably like a miniature crab. Pubic lice are a different species from head lice or body lice, and while they’re not dangerous, they cause persistent itching and are easily passed between people through close physical contact.
What Pubic Lice Actually Are
Pubic lice are extremely small insects, roughly 1 to 2 millimeters long, that live on coarse hair. They’re most commonly found in pubic hair, but they can also show up on chest hair, armpit hair, beards, eyebrows, and even eyelashes. They cannot live on the smooth hair of your scalp because their claws are shaped to grip thicker, more widely spaced hairs.
These parasites go through three life stages: egg, nymph, and adult. The eggs (called nits) are tiny, oval-shaped, and cemented to individual hair shafts close to the skin. They hatch after about a week, and the emerging nymphs go through three molts before reaching adulthood. Adults survive by piercing the skin and feeding on small amounts of blood several times a day. They can’t jump or fly, and they die within one to two days if they fall off a human host.
How Crabs Spread
Pubic lice spread primarily through intimate, skin-to-skin contact, usually during sex. The lice crawl from one person’s body hair to another’s when the hair is in close, sustained contact. Condoms do not prevent transmission because the lice live on the skin and hair surrounding the genitals, not on the genitals themselves.
Non-sexual transmission is possible but much less common. Sharing bedding, towels, or clothing with someone who has an active infestation can occasionally spread lice. Catching them from a toilet seat is technically possible but extremely rare, since the lice would have to have been left behind moments earlier and they don’t survive long away from the warmth of a body.
Symptoms to Recognize
The most common symptom is itching in the pubic area, which usually starts about five days after infestation. The itching comes from an allergic reaction to the lice’s saliva as they feed, and it tends to get worse at night. Some people experience only mild irritation, while others find it intense enough to disrupt sleep.
If you look closely, you may be able to spot the lice themselves clinging to hair shafts, though they’re small enough to be easy to miss. Nits are even harder to see: they look like tiny pale dots glued to individual hairs near the skin. Other visible signs include small blue-grey spots on the skin where the lice have been feeding. These discolored marks, caused by a reaction to the lice’s saliva breaking down blood, can appear on the inner thighs, lower abdomen, or anywhere the lice are active. You might also notice tiny dark specks in your underwear, which are lice droppings.
How Crabs Are Treated
Over-the-counter lice-killing lotions or shampoos containing permethrin are the standard first-line treatment. You apply the product to all affected areas (not just the pubic region, but anywhere you see lice or nits), leave it on for the time specified on the label, and then rinse. If you still see live lice 9 to 10 days later, a second treatment is needed to catch any lice that hatched from surviving eggs after the first round.
After treatment, you’ll want to go through the affected hair with a fine-toothed nit comb to physically remove dead lice and remaining eggs. This step matters because the eggs are glued firmly to the hair and won’t wash away on their own, and some may survive the initial treatment.
If over-the-counter products don’t work, which can happen when lice have developed resistance, a doctor can prescribe stronger options. These include a topical lotion that’s applied and left on for 8 to 12 hours, or an oral medication that kills lice from the inside. The oral option has limited ability to kill eggs, so it typically requires a repeat dose 7 to 14 days later.
When pubic lice end up on eyelashes, which is uncommon but does happen, treatment looks different. Standard lice shampoos are too harsh for the eye area. Instead, the typical approach is applying petroleum jelly to the eyelashes and eyelid margins two to three times daily for 7 to 10 days, which suffocates the lice. An antibiotic ointment may be added if scratching has caused a secondary infection.
Cleaning Your Home and Belongings
Treating your body is only half the job. Any bedding, towels, or clothing you’ve used in the two days before treatment should be washed in hot water (at least 130°F or 50°C) and dried on high heat for at least 20 minutes. Items that can’t be washed, like pillows or stuffed items, can be sealed in a plastic bag for two weeks. Since lice die within a couple of days without a host, anything sealed away that long will be safe to use again.
Sexual partners from the previous month should be notified and treated at the same time, even if they don’t have symptoms yet. Reinfestation from an untreated partner is one of the most common reasons people think treatment “didn’t work.”
Crabs and Other STIs
Pubic lice are classified as a sexually transmitted infection because of how they typically spread. Having crabs doesn’t automatically mean you have other STIs, but the same type of contact that transmits pubic lice can also transmit other infections. For that reason, getting tested for other STIs after a diagnosis is a reasonable step.
Why Crabs Have Become Less Common
Pubic lice infestations have dropped significantly over the past two decades, and grooming trends appear to be a major factor. The widespread popularity of pubic hair removal that began around the early 2000s effectively destroyed the habitat pubic lice depend on. The British Association of Dermatologists has noted that this cultural shift, sometimes called the “Sex and the City factor,” put pubic lice “under considerable strain” and drove infestations to historic lows during the first decade of the century.
As attitudes toward body hair have shifted again, with less social pressure to remove pubic hair, dermatologists have predicted a potential rebound. That said, the same experts have pointed out that the skin problems caused by aggressive hair removal, like ingrown hairs and irritation, are actually more common and represent a greater health burden than pubic lice ever did.