Head and body lice mature into adults and begin laying eggs seven to 10 days after hatching. Pubic lice become adults after four to six weeks.
Adult female lice lay around six eggs, or nits, per day. Each egg is attached with a glue-like material that cannot be easily washed away. If the eggs are fertile, they develop over the course of nine days. Louse eggs do not move, grow or irritate the host until they hatch. Once they develop, young lice, or nymphs, break free from their eggs and crawl onto the hair, leaving behind an empty eggshell. This shell cannot produce more lice, but will remain attached to hair until cut or broken off.