Everything You Need To Know About Head Lice

By: John Robersts

I’ve heard about a few cases of head lice now that kids are back in school and the weather is cooling down. Head lice are white, and about the size of a sesame seed. They are known as obligate ectoparasites. Obligate means they require a placental mammal like a human host to survive and ectoparasite means they live outside the host’s body. Lice must feed on the host’s blood to survive and can’t live off of a body for more than a day or so. They move from person to person by direct head to head or hair to hair contact. They can also spread by sharing personal items such as hats, towels, brushes, helmets, hair ties or even car seat headrests. They do not jump or fly and are not transmitted by pets.

Adult lice survive on a person for about one to three months. A female louse lays about three to five eggs (nits) each day and glues them to the hair shafts of the host close to the scalp. The eggs require the warmth of the scalp to incubate. A louse may lay up to 300 eggs in her adult life. The eggs take about ten days to hatch and the new lice need an immediate blood meal to survive. They then take another seven to ten days to mature to the stage they can start laying eggs.

Lice are not usually harmful to their human host. There is evidence that the head louse is genetically identical to the body louse that is known to carry the organisms causing typhus, trench fever, and relapsing fever. There is some concern that as lice become more resistant to chemical treatments that they will become more prone to spreading diseases, but this is currently not a concern in America.

Screening someone’s head for lice requires a bright light and a good lice comb. Most experts recommend using a fine-toothed comb like the LiceMeister that gets very close to the surface of the hair shafts. Lice like to live on the scalp around the upper neck and backs of the ears. Again, the nits are usually less than one centimeter from the base of the hairs. Dandruff, hair spray residue, and dust can be mistaken for lice and nits.

Treatment of lice requires a lot of patience. There really is no substitute for manual removal using meticulous combing with a lice comb. The patient or parent(s) of a child must take the time to properly comb out every strand of hair to remove the lice and nits. Most experts recommend combing every three days for a couple of weeks. Re-infestations are usually the result of improper removal of lice and nits that hatch later.

Chemical treatments kill live lice, but not the eggs. The treatments therefore have to be repeated in seven to ten days to kill lice after they hatch. Chemical treatments come in two varieties: insecticides and those that suffocate the lice. Insecticides are not benign. They should be used with caution in those with asthma, seizures, brain tumors, cancer, HIV, and pregnant or nursing mothers.

The most commonly used insecticides are permethrin, pyrethrin and malathion. Unfortunately, lice have begun to build up resistance to these agents. Spinosad was approved in 2011 and remains very effective. Some providers prescribe ivermectin that is not FDA approved for the treatment of lice, but is very effective (unlike for COVID).

Benzyl alcohol lotion is the most commonly used suffocation agent that plugs up the breathing pores of the lice. Cetaphil skin cleanser can also be applied to every strand of dry hair, the excess combed out, dried with a hair dryer, and washed out eight hours later. The treatment needs to be repeated at seven day intervals a total of three times.

As far as treatment of a person’s environment, most evidence points to proper treatment of the lice on the person as being the most effective deterrent, not treating their environment. Vacuuming is the best way to remove fallen hairs with attached nits from furniture, rugs, stuffed animals, and car seats. Bagging stuffed animals is not necessary, but they can be run through a hot clothes dryer for 30 minutes along with other linens, hats, etc. to kill lice and nits. Pesticide sprays are not recommended since they do more harm than good.

Family members or other people who live in close contact with someone who has lice should be screened using the LiceMeister comb. Schools have discontinued “no nit” policies due to the very limited risk of transmission in the school setting. Kids should not miss school unnecessarily for infestations that are much more of a nuisance than a health threat.

The best resource I have found for up to date lice information is the National Pediculosis Association at www.headlice.org. Happy hunting!

– Dr. John Roberts is a retired member of the Franciscan Physician Network specializing in Family Medicine.