Head Lice (Pediculosis capitis) is a common infestation found most often in children 3 to 12 years of age. Head lice are not a health hazard, a sign of uncleanliness and are not responsible for the spread of any disease. The adult louse is 2 to 3 mm long (the size of a sesame seed) and is usually light gray, although color may vary. The female can live 3 to 4 weeks and lays approximately 10 eggs, or nits, per day. These tiny eggs are firmly attached to the hair shaft near the scalp with a glue-like substance produced by the louse.
Viable nits are most easily seen at the posterior hairline (near the neck). The eggs incubate using body heat and hatch in 10 to 14 days. Once the eggs hatch, nymphs grow for approximately 9 to 12 days, mate, and females lay eggs. If left untreated, this cycle may repeat itself every 3 weeks. The louse feeds itself by injecting small amounts of saliva and taking small amounts of blood from the scalp every few hours. Lice crawl and are unable to hop or fly. Transmission most often occurs by direct contact with personal belongings of an infested individual (combs, brushes, hats, etc.). Head lice usually survive less than one day away from the scalp and their eggs cannot hatch at ambient temperatures lower than that near the scalp. In general, lice found to be more than 1 inch from the scalp are not likely to be viable.