Head Lice

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Pest Management Fact Sheet #5025

James F. Dill, Pest Management Specialist
Clay A. Kirby, Insect Diagnostician

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Description & Biology

Head Lice
Adult Head Louse

The head louse (Pediculus humanus capitis) is gray in color, but tends to take on the hair color of the host. This insect pest is usually found on the lower back of the head and behind the ears. The female is about 1/16″ to 1/8″ long and flattened in shape; the male is a bit smaller. Hook-like claws at the end of each of six legs help anchor the louse to the hair shaft.

Head lice do not jump or fly.

Hair Shaft with Nit attached (at 40x magnification)
Hair Shaft with Nit attached (at 40x magnification)

A female head louse will live about 30 days on a host. During this period, it will deposit about 90 eggs at a rate of three per day. The grayish-white, 1/16″ long eggs are cemented to hair shafts next to the scalp. The eggs are called “nits” and hatch in about one week. The newly hatched lice (called “nymphs”) molt three times in eight or nine days before becoming adults. The life cycle is completed in about 15 days. During this time, the nymphs–as well as the adults–feed with piercing and sucking mouthparts, injecting saliva to keep blood from clotting. If the lice are not disturbed, feeding may continue for extended periods, and the insects may excrete dark red feces onto the scalp.

The first major symptom of a louse infestation can be intense itching caused by the louse’s feeding, although certain individuals may not experience itching at all. Breaks in the skin caused by the louse and resultant scratching can cause secondary bacterial skin infection, especially in the absence of good hygiene.

Anyone is susceptible to head lice, which can be spread by personal contact or, to a lesser extent, by using an item that has been in contact with an infested person. Examples of such items include bedding, hats, combs, etc. Human lice do not usually infest pets or other animals. Head lice are not known to transmit disease.


To check for infestation, someone must examine the scalp for nits and lice. Examination of children at school requires cooperation and support from pupils and parents. Examiners should use wooden applicator sticks or something similar to part the children’s hair in search of lice or nits. Wipe sticks between exams to lower the unlikely possibility of transmitting head lice from person to person. Nits within 1/2 inch of the scalp are a sign of an active infestation. Nits more than 1/2 inch from the scalp are either infertile or hatched.


Many pediculicides are available to control head lice. They are formulated as creams, shampoos, and lotions. Some require prescriptions, which generally are available from doctors.

Many school nurses have an open prescription for lice medicine. Over the counter pediculicides can be just as effective as prescription pediculicides. Follow directions. Consult a doctor before using the products on infants or during pregnancy. Many pediculicides come with special combs for nit removal.

A person infested with head lice is treated by removing all clothing, applying the pediculicide according to directions, and then getting dressed in clean clothes. Clothes, bedding, and other items contacted by the infested person within 48 hours should be washed in hot water with a detergent and dried in a clothes dryer. Alternate means of dis-infesting articles include dry-cleaning, isolation in a plastic bag for 10 days, or placing items in a freezer. Freezing is lethal to eggs, nymphs, and adults, and so is a temperature of 125F for 30 minutes or more.

To help prevent re-infestation, it is suggested that all family members be treated on the same day. Most products require a repeat treatment 7 to 10 days later. This will kill the lice that hatch after the first treatment. Since head lice cannot live more than two days off the host, and are rarely found off the host, spraying or bombing the premises is of no real benefit.

When Using Pesticides


Pest Management Unit
Cooperative Extension Diagnostic and Research Laboratory
17 Godfrey Drive, Orono, ME 04473
1.800.287.0279 (in Maine)

Information in this publication is provided purely for educational purposes. No responsibility is assumed for any problems associated with the use of products or services mentioned. No endorsement of products or companies is intended, nor is criticism of unnamed products or companies implied.

© 2016, 2018, 2020 | Reviewed: 2023

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