The lice spread more easily in crowded conditions where the distance between people is close, allowing the lice to crawl from one person to another.Infestation on the eyebrows or eyelashes of a child may indicate sexual exposure or abuse. Characteristics and life cycle
Pubic lice (Pthirus pubis) have three stages: the egg (also called a nit), the nymph, and the adult. They can be hard to see and are found firmly attached to the hair shaft. They are oval and usually yellow to white. Pubic lice nits take about 6–10 days to hatch. The nymph is an immature louse that hatches from the nit (egg). A nymph looks like an adult pubic louse but it is smaller. Pubic lice nymphs take about 2–3 weeks after hatching to mature into adults capable of reproducing. To live, a nymph must feed on blood. The adult pubic louse resembles a miniature crab when viewed through a strong magnifying glass. Pubic lice have six legs; their two front legs are very large and look like the pincher claws of a crab—thus the nickname "crabs". Pubic lice are tan to grayish-white in color. Females lay nits and are usually larger than males. To live, lice must feed on blood. If the louse falls off a person, it dies within 1–2 days. Eggs (nits) are laid on a hair shaft. Females will lay approximately 30 eggs during their 3–4 week life span. Eggs hatch after about a week and become nymphs, which look like smaller versions of the adults.
Pediculosis pubis (also known as "crabs" and "pubic lice") is an infestation by the pubic louse, Pthirus pubis, a wingless insect which feeds on blood and lays its eggs (nits) on mainly pubic hair. Less commonly, hair near the anus, armpit, beard, eyebrows, moustache, and eyelashes may be involved. It is usually acquired during sex, but can be spread via bedding, clothing and towels, and is more common in crowded conditions where there is close contact between people.The main symptom is an intense itch in the groin, particularly at night. There may be some grey-blue discolouration at the feeding site, and eggs and lice may be visible. Scratch marks, crusting and scarring may be seen, and there may be signs of secondary bacterial infection.Diagnosis is by visualising the nits or live lice, either directly or with a magnifying glass. Investigations for other sexually transmitted infections (STIs) are usually performed.First line treatment usually contains permethrin and is available over the counter. Two rounds of treatment at least a week apart are usually required to kill newly hatched nymphs. Washing bedding and clothing in hot water kills the lice, and transmission can be prevented by avoiding sexual contact until no signs of infestation exist. Eggs may be removed by combing pubic hair with a comb dipped in vinegar. Sexual partners should be evaluated and treated.Infestation with pubic lice is found in all parts of the world and occurs in all ethnic groups and all levels of society. Worldwide, the condition affects about 2% of the population.