The Facts of Lice


There are a lot of common misconceptions about head lice. In fact, misconceptions are almost as common as head lice themselves.

Here are some facts:
  • Head lice are yellowish-white insects that are about the size of a sesame seed. 1
  • They spread through head-to-head contact.1
  • Lice don't have wings. They do not fly, hop, or jump. But they can crawl quickly!1
  • Lice need human blood to live.1,2 They'll die within 48 hours without it.3
  • It takes about 8 or 9 days for eggs to hatch.1
  • An itchy scalp is the most common symptom of head lice.1,2
  • Mayonnaise, olive oil, margarine, butter, and similar substances have not been proven as effective head lice treatments.1
  • Pets don't get head lice and spread them to people.2

The Life Cycle of the Human Head Louse

Life Cycle of the Human Head Louse

Beginning of the Life Cycle *Photo by Gilles San Martin Head lice begin their life cycle when a female louse lays an egg (nit) and attaches it to a hair shaft.
8 to 10 Days After Life Cycle Starts *Photo by Tabitha Allen Around 8 to 10 days after the nit is laid, it will hatch and a newborn louse will emerge.
 Newly Hatched Louse - Nymph *Photo by Tabitha Allen A newly hatched louse is called a nymph. Nymphs undergo three molts before reaching the adult stage of their lives. Nymphs cannot reproduce. 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.
Adult Stage *Photo by Gilles San Martin After the third molt, a louse has reached the adult stage and can begin to reproduce.

More Facts of Lice

  • 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 cannot 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 cannot 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 not just appear out of thin air; they are transmitted through humans and human contact. They 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 attached "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.


1. Frankowski BL, Bocchini JA Jr; Council on School Health and Committee on Infectious Diseases. Clinical report-head lice.Pediatrics. 2010;126(2):392-403.

2. Mumcuoglu KY, Gilead L, Ingber A. New insights in pediculosis and scabies. Expert Rev Dermatol. 2009;4(3):285-302.

3. Takano-Lee M, Yoon KS, Edman JD, Mullens BA, Clark JM. In vivo and in vitro rearing of pediculus humanus capitis (Anoplura: Pediculidae). J Med Entomol. 2003;40(5):628-635