Head lice

• Head lice, as the name suggests, is infestation of the scalp with lice.
• Head lice infestation, or pediculosis, is spread most commonly by close person-to-person contact.
• Dogs, cats, and other pets do not play a role in the transmission of human lice.
• Both over-the-counter and prescription medications are available for treatment of head lice infestations.

Male human head louse

Pathophysiology

• The head louse, or Pediculus humanus capitis, is a parasitic insect that can be found on the head, eyebrows, and eyelashes of people.
• Head lice feed on human blood several times a day and live close to the human scalp. Head lice are not known to spread disease.

Risk factors

Head lice are found worldwide. In the United States, infestation with head lice is most common among pre-school children attending child care, elementary schoolchildren, and the household members of infested children.

Pediculus humanus capitis

=Swimming

• Data show that head lice can survive under water for several hours but are unlikely to be spread by the water in a swimming pool.
• Head lice have been seen to hold tightly to human hair and not let go when submerged under water. Chlorine levels found in pool water do not kill head lice.
• Head lice may be spread by sharing towels or other items that have been in contact with an infested person’s hair, although such spread is uncommon.
• Children should be taught not to share towels, hair brushes, and similar items either at poolside or in the changing room.
• Swimming or washing the hair within 1–2 days after treatment with some head lice medicines might make some treatments less effective.

Morphology

Head lice have three forms: the egg (also called a nit), the nymph, and the adult.

Egg/Nit: Nits are lice eggs laid by the adult female head louse at the base of the hair shaft nearest the scalp.

Nymph: A nymph is an immature louse that hatches from the nit.

Adult: The fully grown and developed adult louse is about the size of a sesame seed, has six legs, and is tan to grayish-white in color. Adult head lice may look darker in persons with dark hair than in persons with light hair.

Signs and symptoms

• Tickling feeling of something moving in the hair.
• Itching, caused by an allergic reaction to the bites of the head louse.
• Irritability and difficulty sleeping; head lice are most active in the dark.
• Sores on the head caused by scratching. These sores can sometimes become infected with bacteria found on the person’s skin.

Lice image

Treatment

• Treatment for head lice is recommended for persons diagnosed with an active infestation.
• All household members and other close contacts should be checked; those persons with evidence of an active infestation should be treated.
• Some experts believe prophylactic treatment is prudent for persons who share the same bed with actively-infested individuals.
• All infested persons (household members and close contacts) and their bedmates should be treated at the same time.
• Some pediculicides (medicines that kill lice) have an ovicidal effect (kill eggs).
• For pediculicides that are only weakly ovicidal or not ovicidal, routine retreatment is recommended.

Prevent re-infestation

Firstline treatment

Over-the-counter Medications Many head lice medications are available “Over-the-counter” without a prescription at a local drug store or pharmacy.

A medical illustration depicting lice.

Pyrethrins combined with piperonyl butoxide;

Brand name products: A–200*, Pronto*, R&C*, Rid*, Triple X*. Pyrethrins are naturally occurring pyrethroid extracts from the chrysanthemum flower. Pyrethrins are safe and effective when used as directed. Pyrethrins can only kill live lice, not unhatched eggs (nits).

Permethrin lotion, 1%; Brand name product:

• Nix*.
• Permethrin is a synthetic pyrethroid similar to naturally occurring pyrethrins.
• Permethrin lotion 1% is approved by the FDA for the treatment of head lice.
• Permethrin is safe and effective when used as directed.
• Permethrin kills live lice but not unhatched eggs.
• Permethrin may continue to kill newly hatched lice for several days after treatment.
• A second treatment often is necessary on day 9 to kill any newly hatched lice before they can produce new eggs.
• Permethrin is approved for use on children 2 months of age and older.Resistance to 1% permethrin has been reported, but its prevalence is unknown.
• If crawling lice are still seen after a full course of treatment contact your health care provider.

Prescription Medications

• The following medications, in alphabetical order, approved by the U.S. Food and Drug Administration (FDA) for the treatment of head lice are available only by prescription.
• Always follow the instructions of your health care provider when administering these medications.
• If crawling lice are still seen after a full course of treatment, contact your health care provider.

Benzyl alcohol lotion, 5%; Brand name product: Ulesfia lotion

• Benzyl alcohol is an aromatic alcohol.
• Benzyl alcohol lotion, 5% has been approved by the FDA for the treatment of head lice and is considered safe and effective when used as directed.
• It kills lice but it is not ovicidal.
• A second treatment is needed 7 days after the first treatment to kill any newly hatched lice before they can produce new eggs.
• Benzyl alcohol lotion is intended for use on persons who are 6 months of age and older and its safety in persons aged more 60 years has not been established.
• It can be irritating to the skin.

Ivermectin lotion, 0.5%; Brand name product: Sklice

• Ivermectin lotion, 0.5% was approved by the FDA in 2012 for treatment of head lice in persons 6 months of age and older.
• It is not ovicidal, but appears to prevent nymphs (newly hatched lice) from surviving.
• It is effective in most patients when given as a single application on dry hair without nit combing.
• It should not be used for retreatment without talking to a healthcare provider.Given as a tablet in mass drug administrations, oral ivermectin has been used extensively and safely for over two decades in many countries to treat filarial worm infections.
• Although not FDA-approved for the treatment of lice, ivermectin tablets given in a single oral dose of 200 micrograms/kg or 400 micrograms/kg repeated in 9-10 days has been shown effective against head lice.
• It should not be used in children weighing less than 15 kg or in pregnant women.

Malathion lotion, 0.5%; Brand name product: Ovide

• Malathion is an organophosphate. The formulation of malathion approved in the United States for the treatment of head lice is a lotion that is safe and effective when used as directed. Malathion is pediculicidal (kills live lice) and partially ovicidal (kills some lice eggs).
• A second treatment is recommended if live lice still are present 7–9 days after treatment.
• Malathion is intended for use on persons 6 years of age and older. Malathion can be irritating to the skin.
• Malathion lotion is flammable; do not smoke or use electrical heat sources, including hair dryers, curlers, and curling or flat irons, when applying malathion lotion and while the hair is wet.

Spinosad 0.9% topical suspension; Brand name product: Natroba

• Spinosad is derived from soil bacteria. Spinosad topical suspension, 0.9%, was approved by the FDA in 2011.
• Since it kills live lice as well as unhatched eggs, retreatment is usually not needed.
• Nit combing is not required. Spinosad topical suspension is approved for the treatment of children 6 months of age and older.
• It is safe and effective when used as directed. Repeat treatment should be given only if live (crawling) lice are seen 7 days after the first treatment.

For second–line treatment only:

Lindane shampoo 1%;

• Brand name products: None available
• Lindane is an organochloride. The American Academy of Pediatrics external icon(AAP) no longer recommends it as a pediculicide.
• Although lindane shampoo 1% is approved by the FDA for the treatment of head lice, it is not recommended as a first–line treatment.
• Overuse, misuse, or accidentally swallowing lindane can be toxic to the brain and other parts of the nervous system; its use should be restricted to patients for whom prior treatments have failed or who cannot tolerate other medications that pose less risk.
• Lindane should not be used to treat premature infants, persons with HIV, a seizure disorder, women who are pregnant or breast–feeding, persons who have very irritated skin or sores where the lindane will be applied, infants, children, the elderly, and persons who weigh less than 110 pounds.
• Retreatment should be avoided.

When treating head lice

• Do not use extra amounts of any lice medication unless instructed to do so by your physician and pharmacist.
• All the medications listed above should be kept out of the eyes.
• Do not use different head lice drugs at the same time unless instructed to do so by your physician and pharmacist.

Prevention

Head lice are spread most commonly by direct head-to-head (hair-to-hair) contact. The risk of getting infested by a louse that has fallen onto a carpet or furniture is very small. Head lice survive less than 1–2 days if they fall off a person and cannot feed; nits cannot hatch and usually die within a week if they are not kept at the same temperature as that found close to the scalp.

The following are steps that can be taken to help prevent and control the spread of head lice:

• Avoid head-to-head (hair-to-hair) contact during play and other activities at home, school, and elsewhere (sports activities, playground, slumber parties, camp).
• Do not share clothing such as hats, scarves, coats, sports uniforms, hair ribbons, or barrettes.
• Do not share combs, brushes, or towels. Disinfest combs and brushes used by an infested person by soaking them in hot water (at least 130°F) for 5–10 minutes.
• Do not lie on beds, couches, pillows, carpets, or stuffed animals that have recently been in contact with an infested person.
• Machine wash and dry clothing, bed linens, and other items that an infested person wore or used during the 2 days before treatment using the hot water (130°F) laundry cycle and the high heat drying cycle. Clothing and items that are not washable can be dry-cleaned OR sealed in a plastic bag and stored for 2 weeks.
• Vacuum the floor and furniture, particularly where the infested person sat or lay. However, spending much time and money on housecleaning activities is not necessary to avoid reinfestation by lice or nits that may have fallen off the head or crawled onto furniture or clothing.
• Do not use fumigant sprays or fogs; they are not necessary to control head lice and can be toxic if inhaled or absorbed through the skin.
• To help control a head lice outbreak in a community, school, or camp, children can be taught to avoid activities that may spread head lice.

Head lice Resources
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