Head lice (Pediculus humanus capitis) are tiny wingless parasitic insects that infest humans. They typically live in the hair and feed on blood from the scalp.
The most common sign of an active infestation is the appearance of lice eggs in the hair, which can resemble dandruff. The eggs are glued to the shaft of the hair follicle in casings called nits, found particularly on the hair behind the ears and back of the scalp.
Infestation is most common in school-aged children with girls being more commonly affected than boys. African-American children are less often affected; this variation is thought to be the result of differences in the hair shaft structure, which may be oval shaped and thus more difficult for a louse to grasp.
Lice are spread through close physical contact, but can also be spread through shared personal items as well. Although lice are generally not dangerous and don’t carry any infectious diseases, they can be extremely irritating and itchy.