The crab louse Phthirus pubis is transmitted by close body contact. The incubation period is usually between five days and six weeks, although some people have a prolonged period of infestation before symptoms appear.
Adult lice infest pubic hairs, body hair in men, and rarely, eyebrows, eyelashes, beards and moustaches. They are not found on head hair. The lice lay eggs (nits) which adhere firmly to the hair shaft. The louse is most commonly found below the waist.
The life cycle of the crab louse is 15 days and the period of infectivity is as long as the lice or eggs remain alive. Contact infectivity is high.