The Life Cycle of the Human Head Louse

Head lice begin their life cycle when a female louse lays an egg (nit) and attaches it to a hairshaft.

newborn louse

Photo by: Tabitha L. Allen

Around 8 to 10 days after after the nit is laid, it will hatch and a newborn louse will emerge. A newly hatched louse is called a nymph. Nymphs undergo three molts before reaching the adult stage of their lives. Nymphs cannot reproduce.


Photo by: Tabitha L. Allen

The nymph in the photo to the left is newly hatched. The red color indicates that this nymph has already fed once. The size of the louse is compared to George Washington’s eye on a $1 bill.

After the third molt, a louse has reached the adult stage and can begin to reproduce.


  • Head lice will not infest your home the way fleas or bed bugs can. They can only survive for a short period of time without a host; at the most from 24 to 48 hours. It is possible for a newborn louse to survive in the environment until shortly after it hatches.
  • Itching is an allergic reaction to the louse’s saliva. Most people, around 60%, are not allergic and do not get the itching that is usually associated with having head lice.
  • Pets can not contract or carry head lice. They are human parasites and can only survive on human blood.
  • A female louse can lay around 6 to 10 eggs (nits) per day. The nits will hatch in about 7 to 10 days. It takes the newly hatched louse another 7 to 10 days to mature and reproduce its own eggs.
  • Head lice usually live up to 30 days when on a host.
  • Head lice do not carry or transmit diseases. The only medical concern is the possibility of a secondary infection due to scratching the bites.
  • They can not jump or fly.They do not have knees to bend for jumping and they do not have wings for flying.
  • Head lice are most commonly spread through direct hair to hair contact, but they can also be transmitted through items such as contaminated clothing and hair accessories. It is possible, but much less likely, that they can be spread through furniture that has been used by an infested person.
  • Head lice do no just appear out of thin air; they are transmitted through humans and human contact. They have have been around since before recorded history. Dried up lice and their nits have even been found on the hair and scalps of Egyptian mummies.
  • A female louse only needs to mate once and can continue to lay viable nits for the duration of her lifespan.
  • Recent studies are showing that lice are becoming increasingly resistant to the chemicals and pesticides commonly found in over the counter, as well as prescription, shampoos. These treatments are not only working less effectively, but they also do not kill the lice eggs.
  • The nits (eggs) must be laid by live lice. You cannot “catch nits.”
  • Nits are small yellowish-white to dark brown, oval-shaped eggs that are “to the side of a hair shaft and glued “at an angle.”
  • Head lice are clear in color when hatched. They quickly develop a reddish-brown color after feeding.
  • Head lice can infest anyone, regardless of personal hygiene. They prefer clean living environments just like we do.
  • A louse can hold its breath for up to 8 hours.