In heavy infestations, they may also infest other hairy areas. Each female louse lays from 50 to 100 eggs, glueing them individually on the hairs near the scalp. The eggs hatch within 5 to 10 days. The complete life cycle from egg to adult takes about 3 weeks. Slight infestations may occur under the best of sanitary conditions, especially with school children.
Heavy infestations are generally a product of crowding.
It is not hard to mistake other objects for nits, particularly where head lice are suspected. The presence of hatched nits is not necessarily an indication of present louse infestation. Hatched eggs are usually flattened, dirty yellowish, and not opalescent. Live eggs, when held between thumb and forefinger, are felt to be rounded and swollen. Eventually, the hatched nits are moved away from the scalp by hair growth unless they are removed mechanically.