• Tuesday Q & A: Some head lice can be resistant to over-the-counter treatments

Mayo illustration of human hair with head liceDEAR MAYO CLINIC: My child’s school has had a lice outbreak for two months. The problem does not seem to be going away. Is it true that some types of lice are resistant to over-the-counter treatments? Are there more potent options to eliminate head lice?

ANSWER: Although they are often effective, over-the-counter treatments for head lice don’t work in all cases. Some strains of lice can be resistant to the over-the-counter treatments. If head lice persist despite treatment at home, then it’s time to ask your doctor about prescription medication alternatives.

Head lice are tiny, wingless, parasitic insects that live and feed on blood from a person’s scalp. Head lice cause a lot of fear, anxiety and concern. Fortunately, although they are a nuisance, head lice don’t carry any transmissible diseases that are dangerous.

Head lice can spread easily. They may go from one person to another through direct contact, or they may be passed through shared items, such as combs, brushes and towels. Head lice tend to stay within about an inch of the scalp, anchoring onto a hair shaft. If you suspect that you or a family member has head lice, the best places to look are behind the ears and along the back of the neck, near the scalp. Lice are very small, about the size of a strawberry seed. Their eggs, or nits, resemble tiny pussy willow buds. Nits can be mistaken for dandruff, but they can’t be easily brushed out of hair.

Because head lice move rapidly through groups that have close contact, schoolchildren are often affected. Prompt treatment is important to minimize spread within these groups. There are a variety of over-the-counter treatments for head lice. The most common are shampoos containing medications such as pyrethrin or permethrin to kill the lice.

To catch the full life cycle of head lice, treatment should be used more than once. Using only one treatment will not affect head lice that are still in egg form. To be most effective, treatment should be repeated seven or eight days after the first application.

As you have found, however, some lice strains have become resistant to these medications. If you try over-the-counter treatments and they don’t work, consider prescription treatment options.

Malathion is a prescription medication for head lice that you apply to the hair and then rub into the hair and scalp. Benzyl alcohol lotion is a newer prescription treatment for head lice. You apply it to the scalp and hair for 10 minutes and then rinse it off. Seven days later you repeat the treatment. This medication is not recommended for children younger than 6 months of age.

Lindane is a prescription shampoo that’s sometimes prescribed for head lice. However, due to increasing resistance of lice to this medication and to the possibility of serious side effects, lindane typically is used only when other measures fail.

If you don’t want to use medications that kill head lice, you can try using a fine-toothed comb or nit comb to physically remove the lice from wet hair. For this method to be effective, however, it needs to be repeated every three to four days for at least two weeks. It can be difficult to remove all the lice and nits this way.

Home remedies such as putting mayonnaise, oils or petroleum jelly on the scalp to suffocate head lice are rarely effective. Some people try to kill head lice with heat, using an extra-hot hair dryer. Putting kerosene on the hair is also sometimes used in an attempt to kill lice. These techniques can lead to severe burns. Do not use them.

If you cannot get rid of head lice with non-prescription treatment, talk to your doctor. Prescription treatments are available that can often effectively eliminate the problem. Dawn Davis, M.D., Dermatology, Mayo Clinic, Rochester, Minn.


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