U.S. investigators are warning that drug-resistant head lice have been found in at least 25 states, and the bugs are expected to spread even further across the nation.
Permethrin, part of the pyrethroid class of insecticides, has been used to fight head lice, mosquitoes, bedbugs, and other insects for years. Researchers say overuse of the drug has caused head lice and other insects to develop genetic mutations that make them completely resistant to permethrin. 
“It’s a very classic resistance story,” said study lead author Kyong Yoon, an assistant professor in the biological sciences and environmental sciences program at Southern Illinois University in Edwardsville.
“Permethrin products were introduced to U.S. consumers in the early ’90s,” Yoon said. “But the first registered problem was reported from Israel in 1995, probably because they had it in use even earlier. Then in 2000 we found genetic mutations causing resistance in head lice here.”
Head lice are spread through direct physical contact. The critters attack the neck, suck the blood, and attach their eggs to the base of hair shafts. Even though lice don’t jump or fly, they cause an itchy scalp. Fortunately, they are not known to transmit disease.
In the U.S., approximately 6 million to 12 million children are infected with head lice each year. Yoon says parents dole out about $350 million annually on permethrin-containing, over-the-counter and prescription drugs. The tiny parasites have long been associated with poor hygiene, but they can affect anyone of any socioeconomic status.
So far, 25 states have tested positive for the genetically mutated lice, but results from several other states are still pending. According to Yoon, the majority of the lice are 100% immune to the effects of permethrin, a realization the scientist called “really alarming.”
Completely-resistant bugs have been located in:
- North and South Carolina
Partially-resistant bugs have been found in:
- New Jersey
- New Mexico
- New York
For whatever reason, permethrin is still effective at killing head lice in Michigan – scientists aren’t sure why.
Parents who fear their youngsters will come home from school riddled with monster head lice that refuse to surrender their grip should continue to sleep easy at night: prescription medications that don’t contain permethrin are still powerful, effective lice-killing drugs. Lindane shampoo, for especially difficult cases, also works. They cost more, but they still do the job.
“Prescription drugs will be pricier. But if you try and save time and money and treat it on your own it will probably get worse rather than better,” Yoon said.
But if applying pesticides to your head sounds dangerous, you’re right – it is. The pesticide lindane, for example, is a neurotoxin known to cause cancer and damage the reproductive and hormonal systems. Lindane was even recently declared lindane a carcinogen.
There are home remedies for head lice, without the risk of resistance, brain damage, cancer, or any other horrible side effect you can think of. Here are just a few:
Combing wet hair with a fine-toothed nit comb may remove lice and some nits. This method is often how lice are discovered to begin with. The wet hair should be lubricated with something like conditioner, and the entire length of the hair – from scalp to ends – should be combed at least twice per session. Repeat every three to four days for at least two weeks until no more lice are found.
2. Essential Oils
Tea tree oil, anise oil, ylang ylang oil and nerolidol have all been shown in studies to have a toxic effect on lice and eggs.
3. Smothering Agents
Applying products like mayonnaise, olive oil, butter or petroleum jelly to the scalp deprive the lice and eggs of oxygen. The products are simply applied to the hair, covered with a shower cap and left on overnight.
 Mayo Clinic
Julie Fidler is a freelance writer, legal blogger, and the author of Adventures in Holy Matrimony: For Better or the Absolute Worst. She lives in Pennsylvania with her husband and two ridiculously spoiled cats. She occasionally pontificates on her blog.