Nit-Picking With Malice Aforehead

What to do when there’s a louse in the house, or more likely many

By Shelley Herron   |   March 05, 2018

It’s the phone call that parents dread — the school office urging you to pick up your child due to suspected head lice — followed by a sheepish rush to the drugstore for an over-the-counter (OTC) medication.

head lice

A male human head louse (Pediculus humanus capitis). Image courtesy of Gilles San Martin

While these OTC products can work, they are now only about 25 percent effective due to drug resistance in most states, including California, according to Christina Mnatzaganian, PharmD, assistant clinical professor in the Skaggs School of Pharmacy and Pharmaceutical Sciences at UC San Diego.

Still, they are the first line of defense. The two most common OTC medications for lice, which include the active agents permethrins and pyrethrins, are:

  • Nix (permethrin) is a cream rinse applied to wet hair, leaving a residue that kills lice even after they hatch from their eggs (or nits). One treatment might do the trick, but if lice or nits remain, another treatment can be given seven to ten days later, said Mnatzaganian. With Nix, shampoos with conditioners or silicone-based additives should be avoided for about ten days after a treatment since they can make the residue less likely to work.
  • Rid (pyrethrins, piperonyl butoxide) is applied to dry hair with a second treatment required after seven to ten days. Rid (or other products with these active ingredients) should not be used if someone has a chrysanthemum allergy.

Both products are best applied while standing at a sink and then rinsed out under a faucet. In the shower, the pores open in warm water and the product can enter the skin. Overall, both are well-tolerated but can lead to scalp sensitivity, irritation and redness.

“After any kind of treatment, it’s important to use a nit comb to remove the nits (eggs) that might remain before they hatch into lice,” Mnatzaganian said. The nervous system of a louse inside of an egg takes several days to develop so the medications may not be effective on the eggs, which makes manually removing them crucial.

Lice are usually contracted through head-to-head contact, or less commonly, through indirect means, such as sharing of hats/helmets or hairbrushes and accessories, as well as headphones. They don’t jump or fly, contrary to popular belief.

“Everyone else in the house should be checked for lice. If you see a nit or actual louse on a family member’s scalp, you should treat him or her,” said Mnatzaganian, noting that lice only live for 24 to 48 hours once detached from the human scalp so extreme cleaning at home is not required. If a person with lice shares a bed or pillow with others, they should be checked and linens belonging to the lice-infected person should be washed in hot water of at least 130 degrees Fahrenheit.

“Sometimes people treat for lice when what they find is dandruff or lint,” Mnatzaganian said. “This can lead to over-treatment and subsequent resistance to medication. Lice can be hard to see, especially in lighter-colored hair. However, a nit sticks to the hair shaft and is usually found within one centimeter of the scalp. Try brushing it off to ensure it’s really lice.”

If you have tried one of these products twice and it didn’t work, it’s time to see your child’s pediatrician for topical prescription medications, such as Natroba (spinosad) or Sklice (ivermectin) or others drugs that are less commonly used. Each has pros and cons, and they are appropriate for children of varying ages.

Other treatments that some people try but have not been clinically proven include essential oils or applying petroleum jelly or other fats to the head and then covering it with plastic or a shower cap to try to suffocate the lice. In addition, private lice treatment centers are available that use a process called AirAllé®, which uses controlled heat to kill lice, but it can be very expensive, Mnatzaganian said.


To learn more about the featured medical specialties, please visit: