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INTRODUCTION — There are three types of lice that infest humans (figure 1):
●The head louse
●The body louse
●The pubic louse or "crab"
Head lice are usually spread from one person to another through casual contact. Although head lice can be unpleasant, there are effective treatment options available. It is important to find and treat lice quickly to avoid spreading them to others.
This article discusses the diagnosis and treatment of head lice. Pubic lice are discussed separately (see "Patient education: Pubic lice (Beyond the Basics)"). A more detailed discussion of head lice is available by subscription. (See "Pediculosis capitis".)
HEAD LICE DESCRIPTION — The head louse is a tiny, grayish-white insect. Female head lice typically live for about one month and lay 7 to 10 eggs (called nits) per day. The eggs are attached to the base of a hair, near the scalp. The eggs hatch after about eight days.
After the eggs hatch, the egg cases become easier to see. Since the eggs are firmly attached to the hair, they move away from the scalp as the hair grows. Head lice do not jump or fly, and they cannot spread from person to person by attaching to pets.
Direct contact with the hair of a person with lice (hair to hair contact) is thought to be the most common method of spreading head lice. The degree to which contact with objects used by people with head lice, such as clothing, bedding, combs, or brushes, contributes to the spread of head lice is unclear.
Head lice often affect children. In one study, approximately one of every four elementary-level students in the United States had head lice. Black children are affected much less frequently than whites and others in the United States, and males less than females; the reasons for this are not known.
HEAD LICE SYMPTOMS — Most people with head lice do not have any symptoms. Some people feel itching or skin irritation of the scalp, neck, and ears. This is caused by a reaction to lice saliva, which the lice inject into the skin during feeding.
HEAD LICE DIAGNOSIS — Head lice are diagnosed by examination of the scalp and hair (picture 1). Special "nit combs" can be used to assist with the diagnosis.
●Before using the fine-toothed comb, use a regular brush or comb to remove tangles. This can be done while the hair is wet or dry. If the hair is wet, apply hair conditioner to make the hair easier to comb.
●Place the fine-toothed comb at the top of the head, touching the scalp. Pull the comb through the hair from roots to ends. After each stroke, carefully examine the comb for lice or eggs.
●Comb the entire head at least twice.
Finding eggs (nits) without lice does not necessarily mean that there is an active infestation; nits can be found for months after lice are treated. Because lice lay eggs at the base of the hair shaft, the identification of nits within ¼ inch of the scalp suggests (but does not confirm) an active infestation.
Lice can be more difficult to see than nits since they can move and hide from view. A doctor or nurse can examine the head under a special lamp, which causes nits to glow a pale blue color. If you are unsure whether your child has lice, make an appointment for your child to be examined before you start treatment.
Finding head lice can be upsetting to children and parents, but it is important to keep the following in mind:
●Head lice are not a sign of being dirty or sick.
●You can get rid of head lice with proper treatment.
●There are no serious or long-term health problems associated with head lice.
HEAD LICE TREATMENT — There are several options for getting rid of head lice, including creams and liquids, combing, and oral medicine (pills). It is important to follow directions carefully to be sure that the treatment works.
If you are sure that your child (over age two years) has head lice, you can use a nonprescription lice treatment (see 'Insecticides' below). Examine family members and close contacts at the same time and treat them if needed. If your child is under age two years, contact the child's doctor or nurse for treatment advice.
Insecticides — A topical insecticide (pediculicide) is a substance, usually a lotion or gel, that is applied to the scalp to kill lice. Available insecticides include:
●Permethrin (Nix)
●Pyrethrin (RID, A-200, Pronto, Triple X, R&C)
●Malathion (Ovide, prescription required in the United States)
●Benzyl alcohol (Ulesfia, prescription required)
●Spinosad (Natroba, prescription required)
●Topical ivermectin (Sklice, prescription required)
How to use — Only one insecticide treatment should be used at a time. Follow the manufacturer's instructions for applying the insecticide carefully. You should also avoid use of hair conditioner or shampoo-conditioner combination products before application of the insecticide.
Most insecticides are rinsed or washed out of the hair after 10 minutes; however, malathion (Ovide) should be left on the scalp for 8 to 12 hours or overnight. Clean clothing should be put on after an insecticide treatment. Hair should not be rewashed for at least one to two days after use of insecticides.
Malathion has a bad smell, which can be hard for some people to tolerate. Malathion is also flammable and should never be applied in close proximity to fire or electric heat sources (such as a lit cigarette, curling iron, or hair dryer).
Use of a nit comb to remove lice and nits after treatment may help to decrease risk for reinfestation. Nit combing can be performed every two to three days for two to three weeks. Nit combing is not considered necessary after treatment with spinosad.
When to treat again — A few live lice may be seen 8 to 12 hours after using an insecticide, and there is no need to immediately reapply the insecticide if they are moving slower than they were prior to treatment. However, if lice are as active as before treatment, the treatment may not be effective. A health care provider can provide guidance regarding the selection of a new treatment.
Some insecticides must be applied twice to be effective.
●A second treatment is needed with permethrin, pyrethrin, and benzyl alcohol seven to nine days after the first treatment. This is because some lice are able to survive the first treatment.
●A single application of malathion often is sufficient. However, malathion should be reapplied if live lice are seen seven to nine days after treatment.
●Treatment with spinosad should be repeated if live lice remain after seven days.
●Topical ivermectin is given as a single treatment; patients should consult with a healthcare provider before repeating treatment.
Wet-combing — Wet-combing is a way to remove lice from the hair with careful and repeated combing. It is a good option for treating very young children or if you want to avoid using insecticides. However, wet-combing is time consuming and must be repeated multiple times over a period of a few weeks.
Wet the hair and add a lubricant, such as hair conditioner or cream rinse, vinegar, or olive oil. Use a fine-toothed comb to comb through the hair. A lice comb may be provided in the lice medication package, or a flea comb can be used. See above for a description of how to wet-comb. (See 'Head lice diagnosis' above.)
The combing session should take 15 to 30 minutes, depending on the length and thickness of the hair. Comb every three to four days for two weeks after you find any large, adult lice.
Oral medicines — A medicine taken by mouth called ivermectin might be prescribed for people whose lice are resistant to topical insecticide treatment.
Other medications — Other medications for the treatment of lice are being studied and may become available in the future.
Treatments not recommended — Studies have examined lotions and other materials (olive oil, butter, mayonnaise, petroleum jelly [Vaseline]) that are applied to the head, and then allowed to dry, with the goal of suffocating lice. However, lice are difficult to suffocate; wet-combing probably works as well and is less messy.
Lice treatments that use gasoline or kerosine are toxic and can lead to serious injury and should not be used.
Because there is no evidence that these treatments are predictably effective, we do not recommend any of these treatments.
PREVENTING HEAD LICE SPREAD — Adults and children who live with a person diagnosed with lice should be examined for lice and treated if needed. Anyone who sleeps in the same bed should be treated for lice, even if no lice or eggs are found.
School policies differ about who at a school, if anyone, needs to be informed when a child has lice. A confidential call or visit with the school nurse is a good place to start. Most experts believe that children with head lice do not need to be removed from school. Hats and grooming aids, such as brushes and combs, should not be shared.
Clothing, bedding, and towels used within 48 hours before treatment should be washed in hot water and dried in an electric dryer on the hot setting. Dry cleaning is also effective. You can use a vacuum to clean furniture, carpet, and car seats. Items that cannot be washed or vacuumed can be sealed inside a plastic bag for two weeks. Items that the person used more than two days before treatment are not likely to be infested because head lice cannot survive off the body for more than 48 hours. You do not need to have your home or belongings sprayed with insecticide.
WHERE TO GET MORE INFORMATION — Your healthcare provider is the best source of information for questions and concerns related to your medical problem.
This article will be updated as needed on our website (www.uptodate.com/patients). Related topics for patients, as well as selected articles written for healthcare professionals, are also available. Some of the most relevant are listed below.
Patient level information — UpToDate offers two types of patient education materials.
The Basics — The Basics patient education pieces answer the four or five key questions a patient might have about a given condition. These articles are best for patients who want a general overview and who prefer short, easy-to-read materials.
Patient education: Lice (The Basics)
Beyond the Basics — Beyond the Basics patient education pieces are longer, more sophisticated, and more detailed. These articles are best for patients who want in-depth information and are comfortable with some medical jargon.
Patient education: Pubic lice (Beyond the Basics)
Professional level information — Professional level articles are designed to keep doctors and other health professionals up-to-date on the latest medical findings. These articles are thorough, long, and complex, and they contain multiple references to the research on which they are based. Professional level articles are best for people who are comfortable with a lot of medical terminology and who want to read the same materials their doctors are reading.
Approach to the patient with a scalp disorder
Pediculosis capitis
Pediculosis corporis
Pediculosis pubis and pediculosis ciliaris
The following organizations also provide reliable health information.
●National Library of Medicine
(https://medlineplus.gov/headlice.html, available in Spanish)
●Center for Disease Control and Prevention
(https://www.cdc.gov/parasites/lice/)
●The Nemours Foundation
(https://kidshealth.org/en/parents/head-lice.html)
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