A lice infestation, or pediculosis, is caused by parasites living on human skin. Lice are tiny, wingless insects with sucking mouthparts that feed on human blood and lay eggs on body hair or in clothing. Lice bites can cause intense itching.
There are three related species of human lice that live on different parts of the body:
- Head lice, Pediculus humanus capitis
- Body lice, Pediculosis humanus corpus
- Pubic lice, Phthirus pubis, commonly called "crab") lice
Pediculosis capitis is an infestation of head lice. A body lice infestation is called pediculosis corporis. Pediculosis palpebrarum or Phthiriasis palpebrarum, caused by crab lice, is an infestation of the eyebrows and eyelashes.
Lice infestations are not usually dangerous. However, head lice infestations present a serious public health problem because they spread easily among schoolchildren. In general, lice infestations occur in crowded, unsanitary facilities, including prison, military, and refugee camps. Lice infestations also occur frequently among the homeless.
Lice are transmitted through personal contact or infected clothing, bedding, or towels. Pubic lice are sexually transmitted. Lice do not jump, hop, or fly and they do not live on pets.
Head lice infestations are extremely common among children in schools, childcare facilities, camps, and playgrounds. They are the second most common communicable health problem in children, after the common cold, and appear to be on the increase. Six to 12 million American children get head lice every year. In developing countries, more than 50% of the general population may be infested. Head lice can affect anyone, regardless of race, sex, socio-economic class, or personal hygiene. However children aged three to ten and their families are most affected. Girls and women are more susceptible than boys and men. Although American black children are much less likely to have head lice than white or Hispanic children, the incidence is increasing, particularly in black children with thick, kinky hair or hair extensions or wraps. In Africa, head lice have adapted their claws to the curly, elliptical hair shafts of blacks. In developing countries, head lice infestations are a significant cause of contagious bacterial infections. Neither frequent brushing nor shampooing nor hair length affects the likelihood of head lice infestation.
Head lice live and crawl on the scalp, sucking blood every three to six hours. Their claws are adapted for clinging to hair or clothing. Adult head lice can be silvery-white to reddish-brown. They are about the size of a sesame seed, about 0.6 inches (1–4 mm.) long. Female lice lay their eggs in sacs called nits that are about 0.04 inches (1 mm.) long and are glued to shafts of hair close to the scalp. During her one-month lifespan, a female louse may lay more than 100 eggs. The nymphs hatch in three to 14 days and must feed on blood within one day. Nymphs are smaller and lighter in color than adults and become sexually mature after 9 to 12 days. Head lice cannot survive without a human host for more than a few days at most.
Body lice lay their nits in clothing or bedding. Occasionally the nits are attached to body hair. Body lice nits are oval and yellow to white in color. They may not hatch for up to 30 days. Nymphs mature in about 7 days. Body lice can live without human contact for up to 10 days.
Body lice infestations are usually associated with poor personal hygiene, as may occur during war or natural disasters or in cold climates. Body lice can carry and transmit disease-causing organisms, including those for epidemic typhus, relapsing fever, and trench fever. Trench fever is self-limiting. However, typhus and relapsing fever have mortality rates of five to 10 percent. The elderly are most vulnerable to these diseases.
Pubic lice can survive for one to two weeks without human contact and occasionally are transmitted through infected bedding, towels, or clothing. Pubic lice have large front legs and look like tiny crabs. Females are larger than males. Nits hatch in about one week and the nymphs mature in about seven days. Although pubic lice do not carry diseases, they often are found in association with other sexually transmitted diseases.
Causes & symptoms
Lice are endemic in human populations, spreading by personal contact or contact with infested clothing or other personal items. Lice also can be transmitted when unaffected clothing is stored with infested items. Among children, head lice are commonly transmitted by the sharing of hats, combs, brushes, hair accessories, headphones, pillows, and stuffed toys.
Lice infestations are characterized by intense itching caused by an allergic reaction to a toxin in the lice saliva. The itching can interfere with sleep and concentration. Repeated bites can lead to generalized skin eruptions or inflammation. Scratching or scraping at the bites can cause hives or abrasions that may lead to bacterial skin infections. Swelling or inflammation of the neck glands are common complications of head lice.
Body lice bites first appear as small red pimples or puncture marks and may cause a generalized skin rash. Intense itching can result in deep scratches around the shoulders, flanks, or neck. If the infestation is not treated, complications may develop, including headache, fever, and skin infection with scarring. Crab lice in children may be an indication of sexual activity or abuse.
Lice usually are diagnosed by the itching. However, itching may not occur until several weeks after infestation, if at all. The tickling caused by moving lice may be noticeable. Definite diagnosis requires identification of lice or their nits.
Head lice may cause irritability in children. Scalp irritations or sores may be present. Although head lice in children are usually limited to the scalp, in adults, head lice can spread to eyebrows, eyelashes, mustaches, and beards. An adult louse may be visible as movement on the scalp, especially around the ears, nape of the neck, and center line of the crown—the warmest parts of the head. Since less than 20 mature lice may be present at a given time during infestation, the nits often are easier to spot. Nits vary in color from grayish-white to yellow, brown, or black. They are visible at the base or on the shaft of individual hairs. Applying about 10 ounces (280 grams) of isopropyl (rubbing) alcohol to the hair and rubbing with a white towel for about 30 seconds releases lice onto the towel for identification.
Body lice appear similar to head lice, however they burrow into the skin and are rarely seen except on clothing, where they lay their nits in seams. Over time, body lice infestations can lead to a thickening and discoloring of the skin around the waist, groin, and upper thighs. Scratching may cause sores that become infected with bacteria or fungi.
Pubic lice usually appear first on genital hair, although they may spread to other body hair. In young children, pubic lice are usually seen on the eyebrows or eyelashes. Pubic lice appear as brown or gray moving dots on the skin. There are usually only a few live lice present and they move very quickly away from light. Their white nits can be seen on hair shafts close to the skin. Although pubic lice sometimes produce small, bluish spots called maculae ceruleae on the trunk or thighs, usually it is easier to spot scratching marks. Small, dark-brown specks of lice excretion may be visible on underwear.
Since pediculicides (medications for treating lice) are usually strong insecticides with potential side effects, it is important to rule out other causes of scratching and skin inflammation. The oval-shaped head lice nits can be distinguished from dandruff because they are glued at an angle to the hair shaft. In contrast, flat, irregularly
shaped flakes of dandruff shake off easily. A healthcare professional needs to distinguish between body lice and scabies—a disease caused by skin mites—and between pubic lice and eczema, a skin condition.
Most treatments apply to all types of lice infestation and, particularly with head lice, treatments are an area of great controversy. The questionable safety and effectiveness of allopathic (fighting disease with remedies that produce effects different from those produced by the disease) treatments has spurred the search for alternative therapies. With any type of treatment, itching may not subside for several days.
Most authorities believe that head lice should be treated immediately upon discovery. Before beginning any treatment:
- Test a small scalp section for allergic reactions to the medication
- A vinegar rinse helps loosen nits
- Wash hair with regular shampoo
Treatments for applying to the scalp and hair include:
- Olive oil or petroleum ointment to smother the lice. Cover the head with a shower cap, four to six hours per day for three to four days
- Olive oil (three parts) and essential oil of lavender (one part)
- Herbal shampoos or pomades
- A mixture of paw paw, thymol, and tea tree oil
- A combination of coconut oil, anise, and ylang ylang
- Other mixtures of essential oils
- RID Pure Alternative, a nontoxic, hypoallergenic, dye and fragrance-free product
- A spray containing phenethyl propionate, cedar oil, peppermint oil, and sodium lauryl sulfate (LiceFreee)
- Cocamide DEA (a lathering agent), triethanolamine (a local irritant), and disodium EDTA (a chelator), (SafeTek) is both a nontoxic pediculicide and a conditioner for combing out lice and nits
Cutting the hair or shaving the head may be effective. Aromatherapies also are available. Infested eyelashes and eyebrows should be treated with petroleum jelly for several days and the nits should be plucked off with tweezers or fingernails.
Treatment for body lice is a thorough washing of the entire body and replacing infected clothing. Clothing and bedding should be washed at 140°F (60°C) and dried at high temperature, or dry-cleaned.
A common herbal treatment for pubic lice consists of:
The mixture is applied to the pubic hair once a day for three days. Anyone with pubic lice should be tested for other sexually transmitted diseases.
Neither alternative nor allopathic treatments will kill all lice nits. Hair and pubic lice nits must be removed manually to prevent re-infestation as the eggs hatch. Manual removal alone may effectively treat a lice infestation.
Before removing nits, one of the following procedures may be used:
- 50% vinegar rinse to loosen the nits
- wiping individual locks of hair from base to tip with a cloth soaked in vinegar
- 8% formic acid solution applied to the hair for 10 minutes, rinsed out, and towel-dried
- catching live lice with a comb, tweezers, fingernails, or by sticking them with double-sided tape
- enzymatic lice-egg remover
- Hair should be clean, damp, and untangled
- Hair conditioner should not be used on hair treated allopathically
- Remove clothing and place a towel between the hair and shoulders
- Divide hair into square-inch (six sq.-cm.) sections. Clips or elastics can be used to divide long hair
Nits are manually removed with:
- Any fine-toothed comb, including pet flea combs
- A specialized nit comb (LiceMeister, LiceOut)
- A battery-powered vibrating or anti-static comb
- Baby safety scissors
To comb out nits:
- Comb along each hair section from scalp to tip
- Between each passing, dip the comb in water and wipe with a paper towel to remove lice and nits
- Hold the comb to the light to be sure it is clean
- If necessary, clean comb with a tooth or fingernail brush or dental floss
- Work under a good light, with a magnifying glass if necessary
- Do not rush. Long, thick hair may take an hour to comb out thoroughly
- Wash towels and clothing after combing
- Repeat at least twice a week for at least two weeks
Re-infestation occurs often with all types of lice dueto:
- Ineffective or incomplete treatment
- Chemical-resistant lice
- Failure to remove live nits
- Failure to treat all infected household members, playmates, or partners
- Failure to remove nits from clothing, bedding, towels, or other items
- Re-infestation from another source
Re-infestation with body or pubic lice can be prevented by washing underclothes, sleepwear, bedding, and towels in hot, soapy water and drying with high heat for at least 20 minutes. Clothing infected with body lice should be ironed under high heat. Sexual partners should be treated for public lice simultaneously and should reexamine themselves for several days.
To prevent head lice re-infestation:
- Repeat lice checks and nit removal daily until none are found
- Notify school, camp, or daycare, and parents of playmates
- Check and if necessary treat household members, playmates, schoolmates, school or daycare staff, and others in close contact with an infestation
- Treat combs and brushes with rubbing alcohol, Lysol, or soapy water above 130°F (54°C)
- Wash all bedding, clothing, headgear, scarves, and coats with soapy water at 130°F (54°C) and dry with high heat for at least 20 minutes
- Wash or vacuum stuffed animals and other toys
- Vacuum all helmets, carpets, rugs, mattresses, pillows, upholstery, and car seats
- Remove the vacuum cleaner bag after use, seal in a plastic bag, and place in the outside garbage
- Non-washable items should be dry cleaned or sealed in a plastic bag for up to four weeks
- Lice pesticide sprays for inanimate objects are toxic and are not recommended
- Repeat treatment if necessary
All types of lice are treated allopathically with insecticidal lotions, shampoos, or cream rinses. However, experts disagree about the effectiveness and/or safety of pediculicides. Pediculicides do not kill nits, so nit removal and a second application in seven to 10 days may be necessary. Pediculicides can be poisonous if used improperly or too frequently and overuse can lead to the proliferation of chemically resistant lice. The residue may remain on the hair for several weeks and can cause skin or eye irritations.
Pediculicides should not be used:
- Near broken skin, eyes, or mucous membranes
- In the bathtub or shower
- By pregnant or nursing women or children under two
- By those with allergies, asthma, epilepsy, or some other medical conditions
All U.S. Food and Drug Administration (FDA)-approved non-prescription pediculicides contain relatively safe and effective pyrethroids. Insecticidal pyrethrins (0.33%) (RID, A-200) are extracts from chrysanthemum flowers. Permethrin (1%)(Nix) is a more stable synthetic pyrethrin. Pyrethroid pediculicides usually also contain 4% piperonyl butoxide.
To treat with pyrethroids:
- Apply for specified time, usually 10 minutes.
- Thoroughly rinse out.
- Do not wash hair for one or two days after treatment.
- Do not use cream rinse, hair spray, mousse, gels, mayonnaise, or vinegar before or within one week after treatment. These products may reduce pediculicide effectiveness
During the 1990s, as schools began requiring children to be lice and nit-free, the use of pyrethroids rose significantly and the FDA began receiving reports of ineffectiveness. The FDA ordered new labeling of pyrethroid pediculicides on the outside of the carton, in simpler language, and with more information, to take effect in 2005–2006. Permethrin sprays for treating mattresses, furniture, and other items are not recommended.
- Malathion (0.5% in Ovide), a neurotoxic organophosphate, was withdrawn from the U.S. market due to an increase in malathion-resistant lice and re-introduced in 1999. It is foul-smelling and flammable. Sometimes infested clothing is treated with a 1% malathion powder
- Lindane (1% or higher) (Kwell), an organochloride neurotoxin, can induce seizures and death in susceptible people, even when used according to the directions. In 2003 the FDA required new labeling and a reduction in bottle size
- Ivermectin (Stromectol), an oral treatment for intestinal parasites, is effective against head lice but has not been approved for that use by the FDA
Infested eyelashes are treated with a thick coating of prescription petroleum ointment, applied twice daily for ten days.
Despite the presence of chemically resistant lice and the thoroughness required to prevent re-infestation, essentially all lice infestations can be eradicated eventually.
Prevention of lice infestation depends on adequate personal hygiene and the following public health measures:
- Avoid sharing combs, brushes, hair accessories, hats, towels, or bedding
- Check hair and scalp weekly for lice and nits
- Limit sexual partners
Regular lice checks in schools and "no nit" re-entry policies have not been shown to be effective. The American Academy of Pediatrics, the Harvard School of Public Health, and the National Association of School Nurses recommend their elimination, although many healthcare professionals disagree.
Scientists have identified both the gene that enables head and body lice to digest blood and the gene that helps lice combat deadly infections, with the potential for new treatments and preventions for lice infestation.
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Rebecca J. Frey, PhD
Margaret Alic, PhD