A head lice infestation begins with contact with a single louse or nit. The life cycle of head lice involves the adult head lice laying their eggs (nits) in the hair of its human host. The eggs hatch and develop into more adult lice, which then feed on the blood of their host several times a day by biting into the scalp. The lice lay more eggs and the cycle repeats itself indefinitely. When lice bite into the scalp, they leave open sores that can lead to an infection. People who suffer from blood-related medical conditions are especially susceptible.