The life cycle of the head louse lasts 47 to 51 days from the time the egg is laid through adulthood. Adult head lice can live up to 30 days while on their host but only 48 hours if separated from the host.
Head lice prefer the areas of the scalp behind the ears and near the neckline. One sign of their presence is eggs, or nits, glued to the hair shafts. After 8 or 9 days, the nits hatch into nymphs, which metamorphose into adult lice after 9 to 12 days. Both nymphs and adults feed exclusively on human blood. Their bites trigger allergic reactions, causing the characteristic itching of a louse infestation.