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September is head lice awareness month

Jeffrey Hahn, Extension Entomologist

With schools starting recently, you can expect that the number of head lice cases will also increase. What do you need to know if head lice make an unexpected arrival into your home?!

Head lice are pests because they bite and feed on the blood of people. They are annoying and cause itching but fortunately do not transmit any disease. They are found specifically on heads near the scalp at the base of hair shafts. These insects are very small, up to 1/8th inch long (nymphs are smaller). They are grayish or brownish, relatively slender and are wingless. Also look for nits (lice eggs) which are about the size of a pinhead, white and oval and are attached at the base of hair.
Adult head louse. Photo: CDC

Head lice need the warmth of people to survive and are not able to survive off humans for any more than one or two days. These insects do not jump or fly and primarily move from one person to another by direct head to head contact. They can sometimes move to new hosts when infested people share items such as combs, hats, scarves, coats, towels, and similar articles. People that are at the greatest risk from head lice are children and family members in a household with an infested individual.

To help prevent infestations of head lice, children should be taught to avoid sharing combs, brushes, hats and similar items. Heat treat any bedding or clothes that may have been exposed to a person with head lice. This can be done by washing items in hot water (use the hottest setting the clothes or bedding can tolerate) and dry on a high heat. Items can also be bagged and placed in a freezer for one to two weeks to kill any head lice that are present.

If despite your best efforts a family member becomes infested with head lice, there are a few options that can be used to deal with them. Physical removal with a nit comb can help. Nit combs are specially designed to comb through hair, catching lice and nits in the process. This is often a laborious process but is a good supplement before using a shampoo or lotion. Some people will use nit combs when they want to use only a non-chemical method.
There are a variety of insecticidal shampoos and lotions that are available for treating hair to kill head lice. It is critical that they are applied exactly as indicated by the directions. Do not apply a conditioner or a combination shampoo/conditioner before using lice medication. Do not wash treated hair for one to two days. Do not overapply products; do not use them more frequently than what is indicated by the directions.

Two products you can buy over the counter are those that contain permethrin (e.g. Nix) and pyrethrins (e.g. Rid ). A potential problem with these shampoos is that head lice have been shown to be resistant (not be affected) by these products in many parts of the country including Minnesota.

Adult, nymph (immature), and egg (nit) showing
relative size compared to a penny. Photo: CDC
Keep in mind that there are several reasons why it may appear that a treatment did not work: If head lice were misdiagnosed originally and the problem is caused by something else (an expert should examine a sample to verify head lice are present); if a product has not been used properly; if the person becomes reinfested. It is also possible that the head lice are resistant to the medication that is being used. If you suspect a shampoo or lotion containing permethrin or pyrethrins are not killing the head lice (and assuming head lice are confirmed and the product is being used correctly), discontinue using it and try a product with a different active ingredient.

There are some relatively new products that are available by prescription that are effective. Spinosad (e.g. Natroba) kills both head lice and eggs so retreatment is typically not necessary. Malathion (e.g. Ovicide) is effective against head lice and partially so against the eggs. Ivermectin (e.g. Sklice) works well against head lice. It is not considered to be ovicidal (kills the eggs), although it does appear to prevent immature head lice from living for long. Benzyl alcohol (e.g. Ulesfia lotion) kills head lice but does not affect the eggs; this treatment needs to be reapplied seven days after the first one.

Lindane is also available with a prescription. However people are discouraged from using as it is considered a more toxic product.

Don’t use vegetable oil, mayonnaise, or similar material to coat the hair in an effort to suffocate the head lice. This is an unproven method as well being difficult to remove. Also don’t treat a home with insecticides. Head lice are not a household insect problem and treating a home does not help to eliminate a head lice infestation.

For more information see the University of Minnesota publication Head lice and the Centers for Disease Control and Prevention (CDC) web page on head lice.
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