Anju Goel, MD, is board-certified in internal medicine. She has over 10 years of experience in the California public health system addressing communicable disease, health policy, and disaster preparedness.
Head lice is an infestation of tiny, parasitic insects most often found behind the ears and at the back of the neck. Though concerning, lice infestation is not a health hazard—head lice are not responsible for the spread of any disease.
The main symptom of a lice infection is the feeling of something moving around in your hair. As lice are most active at night, this can lead to trouble sleeping. Itching may set in after a few weeks and is caused by an allergic reaction to the louse's saliva. Scratching can lead to a secondary infection, resulting in sores on the scalp.
Over-the-counter treatments and diligent combing to remove lice and eggs (nits) are usually effective.
There are 6 to 12 million cases of head lice in the United States every year among children 3 to 11 years of age. Head lice occur more often in children than in adults.
The first line of treatment for head lice is an over-the-counter anti-lice shampoo, which kills adult lice and nymphs (young lice), but not nits (eggs). Follow-up treatment may need to be applied seven to 10 days after the initial treatment. Additionally, wet-combing using a fine-toothed lice comb is also recommended to remove lice and nits.
Head lice is caused by simple head-to-head contact, or when your head touches another person's head who has a lice infestation. Because young children often play closely together, lice outbreaks are often seen in preschools, daycares, and overnight camps. However, lice can spread to people of any age. It's possible that lice are also spread via items like hats or brushes but this is much less common.
Look for head lice at home in a bright room with a magnifying glass and a lice comb. Live lice can move quickly and try to avoid light. Be sure to look closely at the scalp, around the ears, and the back of the neck, near the hairline. An adult louse is about the size of a sesame seed. If lice are found on one person in your household, all members of your household should be checked.
No, head lice move by crawling—they cannot hop, jump, or fly.1 Lice are spread by direct contact with the head of another person. They may also be spread through bedding or clothes, but this is much less common.
An adult louse can live for about 30 days on a person's scalp, but will die in one to two days if it falls off a person.1 Lice develop in three phases: nit (egg), nymph (young adult), and adult louse.
Even after lice treatment and removal, your scalp may still itch for a week or more after lice are gone. This is due to the allergic reaction caused by the louse saliva on your scalp.
Dandruff is a skin condition primarily affecting the scalp, marked by the appearance of flakes of dry skin. Dandruff flakes may be confused for nits, but flakes can be easily moved along the hair shaft and aren't uniform in size, unlike lice nits, which are firmly attached to the hair shaft close to the skull, and are small and oval-shaped.
The egg phase of a louse life cycle. Nits are typically attached firmly to the hair shaft no more than ¼ inch away from the scalp. Nits hatch every eight to nine days and are oval-shaped, yellow-white, and very small.
Pediculus is the genus of the lice organism. An infestation of head lice is called pediculosis.
The skin covering your head (excluding your face), where hair typically grows. Lice live close to the scalp and feed on human blood several times per day.
Meister L, Ochsendorf F. Head lice: Epidemiology, biology, diagnosis, and treatment. Deutsches Ärzteblatt International. 2016;113(45):763-772. doi:10.3238/arztebl.2016.0763
Centers for Disease Control and Prevention. Head Lice: Frequently Asked Questions (FAQs). Updated July 17, 2019.
American Academy of Pediatrics: Healthy Children. Head Lice: What parents need to know. Updated October 29, 2020.
Centers for Disease Control and Prevention. Head lice: Frequently asked questions (FAQs). Updated July 17, 2019.