Many parents, desperate to get rid of a case of lice crawling around in their child's hair, will dash out to the pharmacy to buy Nix or Rid, the most widely sold lice-control products in an estimated $130 million over-the-counter market.

There’s a reason those chemical products are so popular. The American Academy of Pediatrics and the Centers for Disease Control and Prevention on their websites recommend using those pesticides, as well as even stronger prescription-only products, to get rid of the nasty insects. Says you should physically remove them instead.

“There’s no reason for parents to douse their children’s heads in chemicals,” says Urvashi Rangan, Ph.D., director of consumer safety and sustainability for Consumer Reports. “Physically removing lice, while it seems daunting, is safest for your child’s head.”

The over-the-counter products are losing their fight against lice because studies suggest that most of the bugs in the U.S. have evolved to become genetically resistant to the insecticides found in those products. That includes pyrethrum in shampoos such as Rid and the permethrin in creme rinses such as Nix. Pyrethrum is a naturally occurring pyrethroid extract from the chrysanthemum flower, and permethrin is a synthetic form of that drug. Products with those ingredients have been available to consumers for decades.

A study published in the March 2014 issue of the Journal of Medical Entomology found that 99 percent of the head lice collected by school nurses and professional lice combers in 12 states and three Canadian provinces were genetically resistant to permethrin. “It’s not surprising that we are seeing a resistance to these products,” Rangan says. “That’s what happens with insecticides and pests over time.”

And despite the label claims, pyrethrum and pyrethroid-based products have only a marginal ability to kill the eggs that remain attached to the hair shaft after treatment. “They can’t be relied on to kill all lice eggs,” says Michael Hansen, Ph.D., a senior scientist at Consumer Reports. When the makers of Nix were asked for the evidence to support the claim that Nix “kills lice and their eggs,” a lawyer for the company said its labeling is scrutinized by the Food and Drug Administration, but the content behind it is considered “proprietary and confidential.”

Lice are sesame-seed-size wingless insects that feed on human blood. They don’t transmit disease, but their bites cause intense itching, which can lead to sores and possible secondary infections. Lice can crawl from one head to another in seconds when children touch their heads together during play or when they share combs or hats. The affliction is now second only to the common cold when it comes to conditions that affect elementary-school students in North America. The U.S. has 6 million to 12 million cases a year among children 3 to 11 years old.

So what is a parent to do? First, don’t panic, and don’t be mortified. “Anyone can get lice,” Rangan says, including the parents of the children who bring them home. In the U.S., African-Americans are less likely to get head lice because North American lice can’t get a good grip on the tightly curled oval hair shafts common in African-American hair.

If you get a warning letter that lice have been discovered at your child’s camp or school, inspect your child right away. A female louse (singular for lice) can lay five to six tiny pearl-colored eggs, or nits, a day near the base of a hair shaft, especially behind the ears or at the back of the neck, and before you know it a few generations could be living on your child’s head if you ignore the problem.

But a child with a first case of head lice may not notice anything for four to six weeks. That’s generally how long it takes for the immune system to develop sensitivity to louse saliva. There’s a chance that the itching could be caused by eczema, dandruff, or an allergy. But if it is a case of lice, it will not clear up on its own.

Here’s what Consumer Reports’ experts recommend.

1. Look for live bugs:

Use a metal nit comb—not plastic—that is thin-toothed and finely spaced. Combing your child’s hair with conditioner or another lubricant, such as olive oil (wet-combing), is much better than just looking for the bugs on your child’s head, according to a study in the March 2009 Archives of Dermatology.

German researchers compared the two methods on 304 students, ages 6 to 12. They found that wet- combing identified infestations in 91 percent of the cases, compared with about 29 percent for visual inspections on dry hair. “Wet combing is the only useful method if active infestation has to be ruled out,” researchers wrote.

Make sure you work in bright light; during the summer you can do this outside on a sunny day. Otherwise, use a bright lamp. To wet comb, first coat your child’s hair and scalp with conditioner or another lubricant. Use a wide-tooth comb to separate hair into very small sections. Follow with a metal nit comb—not plastic—that is thin-toothed and finely spaced (you can also use a flea comb, available at most drug stores), concentrating on very small sections closest to the scalp.

After each comb-through, move the section over, wipe the comb on a paper towel, and inspect for lice. Seal the paper towels in a resealable plastic bag and dispose. Remember to clean combs in very hot, soapy water.

2. If you find any lice, comb and comb and comb

Consumer Reports’ experts say the safest method of getting rid of lice is to physically remove the insects and their eggs by combing with a lubricant such as a hair conditioner. “The chemicals on the market don’t kill 100 percent of the eggs, most pose some level of risk, like itchy eyes or chemical burns or seizures, and they are unnecessary in most cases compared with physical removal,” Hansen says. The key, he says, is to continue to comb out your child’s hair every day until no live lice are seen and then every few days for about a month.

A study of two “bug busting” campaigns in the United Kingdom showed that persistence pays off: All lice were eradicated when combing-out treatments were extended from 14 days to 24 days.

3. Skip the chemical products

Over-the-counter chemical treatments have become less effective over the years. As a general rule, younger children have thinner skin, making them more susceptible to chemical absorption, and they are more vulnerable to the side effects of pesticides.

As noted above, over-the-counter chemical treatments such as Rid and Nix ($20 each) have become less and less effective over the years as the bugs have evolved to become more resistant to them. And they are marginal at best when it comes to killing lice eggs. Possible side effects of using them include red, itchy, and inflamed skin or difficulty breathing, which may be problematic for people with asthma. The products shouldn’t be used near cats because felines are especially sensitive to this class of drug.

Prescription treatments come with a range of risks or side effects, and the drugs can be expensive. In 2011 the Food and Drug Administration approved a new drug called spinosad (Natroba), a topical treatment for use in children ages 4 and up, that was found to be more effective in killing lice than permethrin, according to two manufacturer-sponsored studies. And it claims to kill lice eggs. Possible side effects were minimal, including skin and eye redness or irritation. But its long-term safety is still under study, and it costs $280 for 4 ounces.

Other prescriptions include:

Benzyl alcohol (Ulesfia): (About $140 for 7.7 ounces) A topical lotion for children 6 months old and older (the safety for people over 60 is not established). It claims to kill live lice but not their eggs. Possible side effects include skin or eye itching, redness, and irritation.

Citronellyl acetate (Lycelle): (About $190 for 3.4 ounces) A topical gel for children 2 and up and people under age 60. It claims to kill live lice and some eggs, but not all. Possible side effects include skin or eye itching, redness, stinging, irritation, and burning.

Ivermectin (Sklice): (About $300 for 4 ounces) A topical lotion for children 6 months and older and people under age 65. It claims to kill live lice but not their eggs. Possible side effects include conjunctivitis, eye irritation, dandruff, dry skin, and a burning sensation on the skin.

Lindane: (About $120 for 2 ounces) This topical lotion is banned in California, and Consumers Union petitioned the Food and Drug Administration to outlaw this neurotoxic, possibly carcinogenic pesticide as a lice treatment in the early 1980s. But it’s still on the market as a prescription drug for lice despite reports of seizures and even deaths from improper use. And it’s the only lice treatment that carries a black-box warning (the worst kind).

Malathion: ($210, generic, and $255, Ovide, for 2 ounces) A topical lotion for children 6 and older. This drug is flammable, so any source of heat, such as a hair dryer, could cause your child’s hair to go up in flames. Possible side effects include second-degree chemical burns. Accidental contact with eyes can result in a mild form of conjunctivitis.

5. Prevent it from spreading

If your child has head lice, all household members and close contacts should be checked and treated if necessary. Also tell your child’s teacher, who can then advise other parents to check their children’s hair and treat them if necessary.

6. Don’t waste your money on shielding shampoos

Katie’s note: I don’t agree with the header “Don’t waste your money on shielding shampoos”. While Lice Shield and other products may have falsely advertised, other products such as the ones we recommend, have been clinically proven to help prevent head lice. Products just need to be properly tested before making claims.

Parents eager to prevent their children from bringing home lice may be tempted to buy a shampoo or spray called Lice Shield, which claims it can prevent or reduce the risk of getting head lice. But the Federal Trade Commission charged its maker, Lornamead, with false advertising in May.

The products and ads for it claimed that citronella and other essential oils used in the Lice Shield line would “dramatically reduce” the risk of head lice infestations, the FTC said. The company claimed that its products, sold at CVS, Rite Aid, Walgreens, WallMart, and other stores, were “scientifically shown to repel head lice.” But it doesn’t have a well-controlled human clinical study to support that claim.

As a result, Lornamead must shell out $500,000 as part of the settlement and is banned from making any similar claims in the future. “As any parent knows, an outbreak of lice can wreak havoc,” said Jessica Rich, director of the FTC’s Bureau of Consumer Protection. “When marketers say their products can be used to avoid these pests, they’d better make sure they can back up their claims.”