Causes

Head lice infect hair on the head. Tiny eggs on the hair look like flakes of dandruff. However, instead of flaking off the scalp, they stay put.

Head lice can live up to 30 days on a human. Their eggs can live for more than 2 weeks.

Head lice spread easily, particularly among school children. Head lice are more common in close, overcrowded living conditions.

You can get head lice if you:

• Come in close contact with a person who has lice
• Touch the clothing or bedding of someone who has lice
• Share hats, towels, brushes, or combs of someone who has had lice

Having head lice does NOT mean the person has poor hygiene or low social status.

Having head lice causes intense itching, but does not lead to serious medical problems. Unlike body lice, head lice never carry or spread diseases.

Symptoms

Exams and Tests

Head lice can be hard to see. You need to look closely. Use disposable gloves and look at the person's head under a bright light. Full sun or the brightest lights in your home during daylight hours work well. A magnifying glass can help.

Part the hair all the way down to the scalp in very small sections, looking both for moving lice and eggs (nits). Look at the entire head this way. Look closely around the top of the neck and ears, the most common locations for eggs.

Treatment is recommended if even one egg is found.

Treatment

Lotions and shampoos containing 1% permethrin (Nix) often work well. They can be bought at the store without a prescription. If these do not work, a doctor can give you a prescription for stronger medicine. Such medicine should be used exactly as directed.

• To use the medicine shampoo, first rinse and dry the hair.
• Then apply the medicine to the hair and scalp.
• After 10 minutes, rinse it off.
• Check for lice and nits again in 8 to 12 hours. If the lice seem active, talk to your healthcare provider before retreating.

Ask your health care provider if you need to treat those who shared a bed or clothing with the person that has had lice.

An important part of treatment is removing the eggs (nits). Certain products make the nits easier to remove. Some dishwashing detergents can help dissolve the "glue" that makes the nits stick to the hair shaft.

• You can remove the eggs with a nit comb. Before doing this, rub olive oil in the hair or run the metal comb through beeswax. This helps make the nits easier to remove.
• Metal combs with very fine teeth are stronger and more effective than plastic nit combs. These metal combs are easier to find in pet stores or on the Internet than in pharmacies.
• Removing eggs may prevent the lice from returning if the medication fails to kill every one of them.
• Treat children and adults with lice promptly and thoroughly.
• Wash all clothes and bed linens in hot water with detergent. This also helps prevent head lice from spreading to others during the short period when head lice can survive off the human body.
• Repeat combing for nits in 7 - 10 days.

Malathion 0.5% in isopropanol is FDA approved for the treatment of head lice. Apply it to dry hair until the hair and scalp are wet. Leave it on for 12 hours. Malathion may be useful for resistant infections.

Treatment can cause significant side effects in children younger than 6 months old, the elderly, and anyone weighing less than 110 lbs (50 kg), especially when the treatment is used repeatedly in a short period of time.

Outlook (Prognosis)

Lice are usually killed with proper treatment. However, lice may come back, especially if the source is not corrected. For example, a classroom with many infected children can cause kids to repeatedly get lice.

When one case is detected in a family or a school or child-care center, every child at that location should be examined for head lice. This can help prevent further spreading.

Possible Complications

Some people will develop a secondary skin infection from scratching. Antihistamines can help relieve the itching. 

When to Contact a Medical Professional

Call your health care provider if symptoms continue after home treatment, or if you develop areas of red, tender skin, which could mean a possible infection.

Prevention

Never share hair brushes, combs, hair pieces, hats, bedding, towels, or clothing with someone who has head lice.

If your child has lice, be sure to check policies at schools, day-care centers, preschools, and nurseries. Many do not allow infected children to be at school until the lice have been completely treated.

Some schools may have policies to make sure the environment is clear of lice. Sometimes, the insects or their eggs get into areas such as carpets. Frequent cleaning of carpets and all other surfaces in child-care centers prevents spread of all types of infections, including head lice.

Alternative Names

Lice - head; Nits; Pediculosis capitis - head lice

References

Morelli JG. Arthropod bites and infestations. In: Kliegman RM, Behrman RE, Jenson HB, Stanton BF. Nelson Textbook of Pediatrics. Philadelphia, Pa: Saunders Elsevier; 2007:chap 667.

Schlossberg D. Arthropods and leeches. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 380.

Diaz JH. Lice (pediculosis). In: Mandell GL, Bennett JE, Dolin R, eds. Principles and Practice of Infectious Diseases. 7th ed. Philadelphia, Pa: Elsevier Churchill Livingstone; 2009:chap 293.

Update Date: 1/24/2012

Reviewed by: Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of Pediatrics, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.