Head Lice Shampoo

During my initial mad scramble for a fix for my kids’ head lice, I quickly gathered that there are two main types of head lice shampoo on the market.

There are shampoos with pesticides in them, which are meant to kill lice by attacking their nervous systems. And there are head lice shampoos containing enzymes, which are meant to disable or kill lice by mimicking their own molting enzymes and dissolving their exoskeletons. (The enzymes also loosen the powerful glue which lice use to attach nits to hair strands.)

Because of my own experience and through my own research, I’ve become convinced that enzyme shampoos are an excellent choice, and that pesticide shampoos should be avoided.

Shampoos with Enzymes

During the last few years, shampoos have become available that contain non-toxic enzymes chosen specifically to attack lice. The enzymes they use are the same or similar to the enzyme the insect produces itself, in order to molt.

These enzymes work by dissolving the exoskeleton of the bugs. (A head louse normally produces the enzyme only when it is molting and already has a new, larger exoskeleton ready to go. So interrupting its life cycle with enzymes at the right time may leave it with no exoskeleton at all.)

The same enzymes work to loosen the nit glue which holds the nits/eggs onto the hair shaft. I found this effect to be particularly striking.

After washing my daughter’s hair with the enzyme shampoo, I took her out on the deck to comb out her hair … and found that nits were literally falling out of her hair before I started combing. So have a towel ready to put around your child’s shoulders right after rinsing, if you use an enzyme shampoo.

The directions for most enzyme shampoos say to leave it in for at least 10 minutes before rinsing out. However, if you have already used permethrin or another pesticide on your child’s head, you may want to leave it in a bit longer. Some veteran parents speculate that certain pesticides may actually harden nit glue.

After my kids’ lice was gone and I started researching head lice further (to put together this site), I noticed that almost all the professional lice removal services seem to use enzymes. (We were so happy with our shampoo, I considered becoming a distributor!)

We used the enzyme shampoo every day for four days. (My daughter was nit-free after the second combing, but I was determined to overdo it rather than risk missing even one small nit.) Then we used the shampoo on my daughter three more times over the next couple of weeks. We never found another nit (and I was looking for them all the time!)

Shampoos With Pesticides

The pesticides in commonly used brands of head lice shampoo (permethrin, pyrethins, malathion, lindane etc.) are poisons. They kill lice by attacking the bugs’ nervous systems. So if you use them, you are putting poison onto your child’s head.

The manufacturers claim that these shampoos are safe to use because the poisons are present in such small amounts that they will not harm the human being whose head is being treated. But that the same small amount will kill head lice, because they are so tiny.

This theory makes sense – to a point. But using its very own logic, we can assume that the smaller the person being treated, the greater the effect (however minimal) of the poison will be. And small children tend to be the ones who get head lice.

The product manufacturers issue warnings NOT to use these products over and over again in a short time frame. That alone sets off red flags to me about the safety of the product.

If it’s dangerous to use a few times in a few days, then I don’t want to even use it once. It’s just safest not to mess around with pesticides applied directly to kids’ heads.

The FDA, the NIH and other authorities have warned about the risk of harm from pesticides commonly used to treat head lice. For more information about this, see our lice treatment warnings page.

Resistant Lice

There’s another serious reason not to use the pesticidal head lice shampoos. They may not even work.

When these pesticides were first developed and marketed, they were very effective at killing head lice.

But over the years, research shows that more and more head lice are proving to be resistant to the pesticides. The parasites have developed the ability to survive treatment with these poisons.

Every time we treat a person with a pesticide that kills some of that person’s head lice, but not all of them, we are contributing to the resistant head lice problem.

It’s very similar to the antibiotic resistance problem that has surfaced in recent years. (Decades of over-prescription of antibiotics have accelerated the ability of the bacteria to develop resistance.)

So, the problem of pesticide-resistant head lice promises to only get worse. The good news is … messing around with dangerous and ineffective pesticides in a head lice shampoo is just not necessary.

So you can put any worries about resistance to bed, and just use a nontoxic enzyme shampoo (that will help remove lice, and loosen the nit glue too). Presumably, insects cannot become resistant to their own enzymes.

See our discussion of head lice prevention for information about shampoos that some people use regularly to prevent head lice.

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