This year you may be among the millions of parents who get the news that their child has lice. If that isn’t bad enough, you’re now going to have a lot more trouble getting rid of them.

The reason? Mutant lice. A study by researchers at Southern Illinois University in Edwardsville found that lice in at least 25 states have developed gene mutations that make them resistant to common over-the-counter lice treatments, rendering the remedies virtually ineffective.

Related: How to Get Rid of Lice

These drugstore lice treatments (RID, A-200 Lice Treatment, R&C Lice Treatment Kit, Pronto Lice Kill System and others) contain the active ingredients permethrin (Nix) or pyrethrins, which are made from chrysanthemum flowers.

Lice have developed three genetic mutations known collectively as "knock-down resistance,” which changes their nervous system and desensitizes them to the drugstore insecticides, according to the study. In 25 of the 30 states the researchers looked at, which ranged from California to Maine, the lice had all three mutations, and in four other states some of the mutations were cropping up. The only state they studied in which the insecticides still worked was Michigan.

“The notion of lice being resistant is old news; it’s been a problem since the mid-1990s,” says Deborah Altschuler, president of the National Pediculosis Association (NPA). (“Pediculosis” means “lice infestation.”) But this study is important, she notes, because it documents how widespread the problem has become.

“Even in their best days before resistance was shown, these products were never 100 percent effective,” says Altschuler. Unfortunately, when they don’t work, parents often re-apply them. This increases the child’s exposure to the insecticides,experts say, and may further increase the chance of resistance.

Some stronger prescription lice treatments still work, but they are more hazardous — and lice can become resistant to them, too.

“If you use a chemical over and over, these little creatures will eventually develop resistance,” said lead researcher Kyong Yoon, PhD, in a news release. “So we have to think before we use a treatment. The good news is head lice don’t carry disease. They’re more a nuisance than anything else.”

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New ways to nitpick

Before you pull out your hair in frustration, here are some tips from experts at the NPA, the American Academy of Pediatrics (AAP) and other organizations on how to get rid of these infuriatingly itchy pests, whether they’re resistant or not.

Make sure that lice are actually causing that itch. The AAP warns that you should never begin treatment until you are sure your child has head lice. This means spotting either the creatures or the tiny nits (eggs) in the hair. If necessary ask your child’s doctor to figure out whether there’s an infestation.

Ask your pediatrician what treatment she recommends. She may know whether lice outbreaks in your area are resistant to common treatments. As long as doctors don’t suspect resistance, she may recommend using an OTC permethrin or pyrethrins medication. (Note: pyrethrins should not be used by people allergic to chrysanthemums or ragweed, or by children under age 2.)

Follow the instructions word for word. Many medications call for a second application after nine days to kill any newly hatched lice before they can produce new eggs.

Avoid over-treatment. The Centers for Disease Control and Prevention warns not to treat someone more than two to three times with the same medication. The NPA goes a step further and recommends you discontinue use of the treatment at the earliest sign of failure and to use nit combs to get rid of the lice by hand.

Avoid Lindane entirely. Doctors sometimes prescribe Lindane shampoo to get rid of lice, but misuse or prolonged use has led to seizures and deaths in some cases, according to the Food and Drug Administration. In June 2015, The World Health Organization classified Lindane as a carcinogen, and the AAP no longer recommends using it. California banned it as a lice-killer in 2002.

Never use a lice spray. Although there are over-the-counter lice sprays on the market, the AAP warns you should never spray pesticides in your home. Altschuler concurs. “Why would you ever spray your child’s bed, where they spend eight hours a day, with a pesticide?” she says.

Comb, comb, comb. According to the NPA, manually removing the eggs and bugs with a nit or lice comb is the surest way to get rid of lice, especially when treatment products have failed. Its experts recommend the Licemeister Comb. Its tiny tines catch both lice and nits. 

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Have someone else do the nit-picking for you. Some cities have seen the advent of hairdressing salons that specialize in combing out lice in kid’s hair. “Lice can live through everything — toxic or not,” says Maria Botham, CEO and founder of Hair Fairies and Pediatric Scalp Care Specialists, based in Los Angeles. “Removing head lice is like changing a tire or painting your own kitchen. You can do it yourself, or avoid that by hiring someone else to do it.” Botham adds that with all the fuss about lice, your child may be distressed and even frightened. She likes to tell children that lice are the friendliest and cleanest bugs out there: “They get shampooed all the time and find new homes when kids are having fun.”

The good old-fashioned buzz cut. You don’t actually have to have your child’s head shaved; a very close-cropped, stylish cut is easy to “nitpick” and will discourage lice just as well.

Don’t delay. “The longer you wait to treat it, the longer it takes to resolve,” says Altschuler. “Parents need to know the importance of catching it early.” 

Mary Purcell is a freelance writer and health researcher in Piedmont, Calif., with expertise in policy analysis. She has a master's degree in Latin American studies from Georgetown University.