According to the American Academy of Pediatrics guidelines, the gold standard for diagnosing an active head lice infestation is the identification of a live nymph or adult louse.
These guidelines recommend an examination of wet hair lubricated with such products as a standard hair conditioner. Your doctor will carefully comb your child's hair with a fine-toothed comb (nit comb) from the scalp to the end of the hair. If no live louse is found, he or she will likely repeat the entire exam at a second appointment.
Your doctor will also look for nits in your child's hair. To find nits, he or she may use a specialized light called a Wood's light, which causes nits to appear bluish. But the identification of nits does not necessarily confirm the diagnosis of an active infestation.
A live nit needs to be near the scalp to incubate. Nits found more than about 1/4 inch (6 millimeters) from the scalp are likely dead or empty. Suspect nits can be examined under a microscope to determine if they're living — evidence of a likely active infestation.
If no live nits are found, they're probably left from a previous infestation and not evidence of an active infestation.
Your doctor will likely recommend an over-the-counter (OTC) medication that kills lice and some of the eggs. These medications may not kill recently laid eggs. Therefore, an appropriately timed second treatment is usually necessary to kill nymphs after they hatch but before they become adult lice.
Some studies suggest that retreating nine days after the first treatment is the ideal time for a second treatment, but other retreatment schedules exist. Ask your doctor for written instructions for a recommended treatment schedule.
OTC medications are based on pyrethrin, a chemical compound extracted from the chrysanthemum flower that is toxic to lice. Wash your child's hair with shampoo with no conditioner before using one of these treatments. Rinsing the hair with white vinegar before washing may help dissolve the glue that holds the nits to the hair shafts. Follow directions on the package for how long to leave the medication in the hair, and rinse your child's hair over a sink with warm water.
OTC medications include the following:
- Permethrin (Nix). Permethrin is a synthetic version of pyrethrin. Side effects may include redness and itching of the scalp.
- Pyrethrin with additives (Rid, A200 Lice Treatment). In this OTC medication, pyrethrin is combined with another chemical that enhances its toxicity. Side effects may include itching and redness of the scalp. Pyrethrin shouldn't be used if your child is allergic to chrysanthemum or ragweed.
In some geographic regions, lice have developed resistance to OTC medications. Also, OTC treatment may fail because of incorrect use, such as not repeating the treatment at an appropriate time.
If the correct use of an OTC treatment has failed, your doctor may recommend a prescription treatment. These include:
- Benzyl alcohol (Ulesfia). This product is not toxic to lice but kills them by depriving them of oxygen. Side effects may include redness and itching of the scalp. The use of benzyl alcohol to disinfect medical devices has been shown to cause seizures and other severe reactions in newborn infants. Therefore, lice treatment with benzyl alcohol is not approved for use in children less than 6 months of age.
- Malathion (Ovide). Malathion is approved for use with people age 6 or older. The medicated shampoo is applied, left to dry naturally and rinsed out after eight to 12 hours. The drug has a high alcohol content, so it can't be used with a hair dryer or near an open flame.
- Lindane. This medicated shampoo has a risk of severe side effects, including seizures, and is used only when other treatments have failed. It is not recommended by the American Academy of Pediatrics for use on children. The Food and Drug Administration (FDA) warns that it should not be used on anyone who weighs less than 110 pounds (50 kilograms), is pregnant or breast-feeding, has a history of seizures, or has HIV infection.
Lifestyle and home remedies
If you prefer not to use a medication for treating a head lice infestation, you may consider an alternative home treatment. There is little to no clinical evidence of the effectiveness of such treatments.
Combing wet hair with a fine-toothed nit comb may remove lice and some nits. Research is inconclusive on the effectiveness of this method.
The hair should be wet, and you should add something to lubricate the hair, such as a hair conditioner. Comb the entire head from scalp to end of the hair at least twice during a session. The process should be repeated every three to four days for several weeks — at least two weeks after no more lice are found.
Small clinical studies have suggested that some natural plant oils may have a toxic effect on lice and eggs. These products include:
- Tea tree oil
- Anise oil
- Ylang ylang oil
- Nerolidol, a chemical compound found in many plant oils
These products are not required to meet safety, efficacy and manufacturing standards used for drugs approved by the FDA.
A number of household products are used to treat head lice infestations. The reasoning is that these products deprive the lice and incubating eggs of air. The product is applied to the hair, covered with a shower cap and left on overnight. Products used for this purpose include:
- Olive oil
- Petroleum jelly
One laboratory study found that of these products, only petroleum jelly was effective in killing a significant number of lice. There is little clinical evidence of the effectiveness of such treatments, and it is unclear whether reported effects are the result of the product or of the multiple washing and combing required for removing the oily products from the hair.
The Lice Clinics of America uses a Food and Drug Administration-cleared machine that uses one application of hot air in an attempt to kill head lice and their eggs through dehydration. The machine requires special training and is currently available only at professional lice treatment centers.
The machine uses air that is cooler than most hair dryers and at a much higher flow rate to kill the lice by drying them out. A regular hair dryer should not be used to accomplish this result as it's too hot and could burn the scalp.
Dangerous products to avoid
Flammable products, such as kerosene or gasoline, should never be used to kill lice or to remove nits.
Lice usually don't live past one day without feeding from a scalp, and eggs do not survive if they aren't incubated at the temperature near the scalp. Therefore, the chance of lice surviving on household items is small.
As a precaution you may clean items that the affected person has used in the previous two days. Cleaning recommendations include the following:
- Wash items in hot water. Wash bedding, stuffed animals and clothing in hot, soapy water — at least 130 F (54.4 C) — and dry at high heat.
- Clean hair care items. Clean combs, brushes and hair accessories in hot, soapy water.
- Seal items in plastic bags. Seal items that cannot be washed in plastic bags for two weeks.
- Vacuum. Give the floor and upholstered furniture a good vacuuming.
Preparing for your appointment
See your family doctor or pediatrician if you suspect your child has head lice. The best practice for determining if a child has an active head lice infestation is the identification of a live nymph or adult louse. Your doctor can carefully inspect your child's hair and, if necessary, examine suspect items under a microscope before confirming a diagnosis of head lice infestation.