Why Head Lice Are More Stubborn Than Ever

CC BY 2.0. Gilles San Martin

These itchy little pests have developed resistance to the most common chemical treatments, making it harder than ever to get rid of infestations.

Every few weeks my kids come home from school with a bright yellow notice stating that lice have been found in a classmate’s hair and we parents should check our kids carefully. It fills me with dread every time, but fortunately we haven’t found any yet. It helps having boys, too, whose heads I would simply shave in the case of an infestation.

Lice are everywhere. In the United Kingdom, an estimated 8 to 10 percent of kids are thought to have lice at any given time, and the United States sees around 6 and 12 million cases a year. Lice travel quickly, up to 23 centimeters (9 inches) per minute. Usually they crawl (they do not hop) between heads during hugs. They require direct contact to transfer, which means that infestation from clothing (hats, scarves, coats) and sleeping in someone else’s bed is uncommon, according to the Centers to Disease Control and Prevention, although it’s still a good idea to launder these items when fighting lice.

What’s frustrating is that lice have developed resistance to many of the treatments that were effective a decade or two ago, and it’s harder than ever to get rid of an infestation. You may recall the bottles of Nix that were touted as the best chemical treatment for lice when we were kids in the 90s. Now things have changed, as described by an article in The Guardian called “Itchy and Scratchy – why the battle against head lice just got serious”:

“Nix was ‘almost 100% effective between its launch [in 1992] and 2000, when lice began to develop resistance ... But by 2014 a study found that the Nix product had become 25% as effective as when it first came on the market’.”

We shouldn’t be surprised. This is what happens to insects and parasites all around the world whenever they’re blasted continuously with high doses of pesticides. They mutate and develop “knockdown resistance to pesticides” in recent years. The Guardian cites University of Massachusetts researcher John Clark, who spent two years walking around with a box of lice strapped to his leg in order to prove these mutations:

“‘We’d seen it many times in agricultural insects,” he says, which is why he dislikes the phrase ‘super lice’: for Clark, they are only doing what lots of creatures have done before.”

Unfortunately the UK government barely regulates the products sold for head lice treatments. They are considered “class 1 medical products,” which means they’re sold everywhere and not subject to independent assessment. Companies are able to market products that are not terribly effective, while government agencies “overlook, defend or support those claims.”

If one wants to try new drugs to which the pests have not yet developed resistance, these often require prescriptions and are exorbitantly expensive if one doesn’t have benefits; but in order to qualify in the U.S., one must have tried an over-the-counter treatment at least twice and be seen by a doctor to confirm its inefficacy before a prescription can be written.

Clark told the CBC: "The efficacy of all those products has gone way down. It started out at 100 per cent; now we're down to 20 to 30 per cent in recent clinical studies.”

So what is a desperate parent to do?

The Guardian describes the proliferation of theories on what works best:

“Scan any parenting forum on the subject and a host of desperate treatments emerge. Some folks slather mayonnaise on to the infested head; olive oil, coconut oil, vinegar. Some believe in electronic combs that beep upon execution, or use a vacuum to suck out the worst. Others apply heated straighteners, then stow bedding in the freezer to kill any off-head survivors. Some swear by dimethicone treatments. Others try them and curse.”

De-lousing clinics are popping up all over the United States and Britain, where you can pay a jaw-dropping £100-199 (US $125-250) to have someone blast your scalp with a dehydrating hot air treatment that kills 99.3% of nits (eggs) and 88% of adult lice. For a low-tech solution, you can hire an expert mother who has honed her skills at combing thoroughly and quickly – a growing cottage industry within the United States.

Alternatively, you can spend your every night for a week slathering your kids’ heads with conditioner, which immobilizes the lice, and going at it with a lice comb – a ton of work, but it’s free. Research shows that nothing beats an old-fashioned comb and hours of patience. Consumer Reports says it's "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." It's a lousy job, but it's got to be done.