The Life Cycle of Head Lice: From Egg to Adult and Everything In-between

Lice start out as eggs or nits that attach to the hair shaft of humans. Lice eggs are oval shaped and range from yellow to white coloring. They are only about the size of a knot in a string and are usually found about ¼ inch down from the scalp. Because the eggs remain in a shell for protection, many lice products have trouble penetrating through and killing the lice. A lice shampoo can be applied later, once the eggs hatch, in order to effectively kill the new lice or a lice egg comb can be used to remove lice eggs before they hatch.

Lice eggs hatch after about a week and lice nymphs emerge. There are three stages of nymph as the lice mature toward adulthood. The lice nymph molts three times after hatching in order to grow into a full sized louse. After the third molt (about 16 or 17 days into the lice’s life) it enters the adult stage and can reproduce.  Adult lice are 2 to 3 mm long or about the size of a sesame seed.

Adult female lice can lay three to eight eggs a day (this is how and why lice infestations escalate so quickly). Lice survive for about another two weeks after reaching adulthood if they remain in a stable environment on the human head. If lice are detached from human hair and fall off they usually die within two days due to lack of food and lack of optimal temperature for survival.

Overall, lice can live for about 30 days on someone’s head. A female louse only needs to mate once in order to produce eggs throughout her life span. In addition, each female louse will average about 125 eggs during its lifespan. It is important to understand the life cycle of lice in order to effectively treat and manage lice infestations. Know what tools are best for each different stage of lice – from lice shampoo to a nit comb.