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Lice Infestation

(Pediculosis)

by James G. H. Dinulos, MD

Lice infestation (pediculosis) is a skin infestation by tiny wingless insects.

  • Lice spread most frequently through close person-to-person contact.

  • People with lice usually have severe itching.

  • Lice and their eggs can be found by looking through hair on the head or other parts of the body.

  • Treatment usually involves shampoos, creams, or lotions and sometimes decontamination of clothing and bedding.

  • Some people require an antiparasitic drug taken by mouth.

Lice are barely visible wingless insects that infest the head, body, or pubic area and live by sucking blood. They spread easily from person to person by close contact and shared clothing and other personal items. Three species of lice inhabit different parts of the body. Head lice and pubic lice live directly on the person, whereas body lice live on clothing and bedding. All types of lice infestation occur worldwide.

A Close-up Look at Lice

Three types of lice infest the body. Lice measure up to 1 / 8 inch (3 millimeters) across.

Head lice

Head lice infest the hair and scalp. The infestation is spread by close personal contact and possibly by shared combs, brushes, hats, and other personal items. Static electricity or wind may eject lice from hair. Head lice are most common among girls aged 5 to 11 but can affect almost anyone. Head lice are rare in blacks. There is no association between head lice and poor hygiene or low socioeconomic status.

Body lice

Body lice usually infest people who have poor hygiene, people who are living in cramped, crowded conditions (such as military barracks), and people who are of low socioeconomic status. They live on clothing and bedding that are in contact with the skin, not on people. Body lice are spread by sharing contaminated clothing and bedding. Unlike head lice, body lice sometimes transmit serious diseases such as typhus, trench fever, and relapsing fever.

Pubic lice

Pubic lice (“crabs”), which primarily infest the hairs in the genital and anal areas, are typically spread among adolescents and adults by sexual contact. They may be transmitted to children by close contact with parents. Pubic lice may also be transmitted by inanimate objects, such as towels, bedding, and clothing. These lice may infest the chest, thigh, and facial (beard, mustache, and eyelashes) hair as well.

Symptoms

Lice infestation usually causes severe itching in the infested area.

Body lice bites cause small, red, pinpoint holes in the skin. People have scratch marks, hives, or, if intense scratching has broken the skin, a bacterial infection. These symptoms are especially common on the shoulders, buttocks, and abdomen.

Pubic lice bites may also cause bluish gray spots to form on the chest, buttocks, and thighs. Lymph nodes can swell. Lice that have infested the eyelashes cause eye itching, burning, and irritation.

Children may hardly notice head lice or may have only a vague scalp irritation.

Diagnosis

Head lice can be found by moving a fine-tooth comb through wet hair from the scalp outward. Lice are usually found at the back of the head or behind the ears. Lice themselves are sometimes hard to find, but their eggs are easier to see. Female lice lay shiny grayish white eggs (nits) that can be seen as tiny globules firmly stuck to the base of hair shafts. Each adult female louse lays 3 to 5 eggs per day, so nits typically greatly outnumber lice. With chronic scalp infestations, the nits grow out with the hair and therefore can be found some distance from the scalp, depending on the duration of the infestation.

Nits are distinguished from other foreign material present on hair shafts by the fact that they are so strongly attached. Adult body lice and their eggs also may be found in the seams of clothing and bedding. Pubic lice can be found by close inspection with an ultraviolet light or by analyzing them with a microscope. Pubic lice may also leave dark brown specks (feces) on the skin or undergarments.

Treatment

Head lice

Several effective prescription and nonprescription drugs are available to treat head lice. Nonprescription shampoos and creams containing pyrethrins plus piperonyl butoxide are applied for 10 minutes and are then rinsed out. Prescription permethrin (a synthetic form of pyrethrin), applied as a liquid or as a cream, is also effective. Lindane—a prescription drug that can be applied as a lotion or shampoo—also cures lice infestation but is not as effective as the other preparations and is not recommended for children under age 2, pregnant or lactating women, or people with a seizure disorder because of possible toxic side effects. Prescription malathion is highly effective at killing both adult lice and eggs, but it is not the first treatment doctors give because it is flammable, has an unpleasant odor, and must remain on the person for 8 to 12 hours. All of these louse treatments are repeated in 7 to 10 days to kill newly hatched lice. Lice have started to become resistant to drugs and may be hard to kill. One dose of the drug ivermectin is usually given by mouth if lice resist standard treatment.

Most drug treatments also kill nits but do not remove them. Dead nits do not have to be removed, but drugs do not always kill all nits. Because it is not usually possible to distinguish between living and dead nits, doctors recommend removing them. In addition, a very small percentage of children with nits in their scalp still have live lice. Removal requires a fine-tooth comb—which is often packaged with the lice removal products—and careful searching (hence the term “nit-picking”). Because the nits are so strongly stuck to the hair, several nonprescription preparations (shampoos, gels, and sprays) are available to loosen them. Thirty minutes under a hot hair dryer may also help kill nits (but not lice). Nits are carried away from the scalp as the hair grows. If there are no nits within ¼ inch of the scalp, the person does not have any live lice. For head lice, doctors do not have good evidence that it is necessary to clean or throw away people’s personal items or to exclude people from school or work. However, many experts recommend that clothing and bedding that is contaminated with the nits of lice be replaced or decontaminated by thorough laundering or dry cleaning. These items should probably be dried in a drying machine that reaches 130° F for about 30 minutes.

Pubic lice

Pubic lice can be treated with nonprescription shampoos and creams containing pyrethrins plus piperonyl butoxide or lindane, as head lice are treated. Sex partners should also be treated. Lice that affect the eyelashes can be treated with petroleum jelly applied for 8 to 10 days, fluorescein eye drops, ivermectin taken by mouth, petrolatum salve, physostigmine ointment, or careful removal of each louse with an instrument.

Body lice

Usually, no drug is used to eliminate body lice because body lice are in clothing and linens and not the person. Doctors treat a person's symptoms and recommend replacing or decontaminating affected clothing and linens by thorough laundering or dry cleaning. It is best to expose these items to heat of at least 149° F during drying.

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