Ask SciMoms: How do you treat head lice?

by Alison Bernstein, posted in Health
Scratching head as if with lice


The summer of 2014 was not pretty in our house. Hybrid #1 (my daughter) came home from camp with lice too many times to count. Thus began the Great Delousing of 2014. In this post, we cover over-the-counter (OTC) and prescription treatments, including dimethicone for lice.

At the time, I was not aware that prescription treatments are available and I did not want to use pesticide-based OTC treatments since I had heard that many lice are resistant. No lice removal is 100% ovicidal (kills eggs) so complete removal of lice requires careful and diligent combing of the hair with special nit combs that capture the nits (eggs) and remove them from the hair, even after treatment. Because we would have to comb no matter what, I did not see an added benefit to using the pesticide-based products. With little added benefit, I didn’t see the point in taking any risk, even if that risk is very small.

We had a local lice removal place that used manual removal so it was a doable option for us. Of course, the manual removal service costs much more than the OTC products so, if that doesn’t fit in your budget, your decision might be different than mine. After visiting the lice removal place a couple of times, I learned to do the combing on my own by watching and asking a lot (too many?) questions. We combed every 3-4 days until no new eggs or lice were found. We were always clear on the 3rd time.

Even now that I know about some of the newer, prescription treatments, I would still do the manual treatment since I would have to do the tedious and repetitive combing anyway (did I mention it’s tedious and repetitive and takes forever if you have a daughter with very thick curly hair?).

That’s my anecdotal experience, now let’s get to the science about some common lice removal remedies you may encounter. For a full review of all possible remedies you may encounter on the internet, you can read this report from the American Academy of Pediatrics (AAP) on Head Lice. Here, I’ve highlighted the treatments commonly recommended amongst parents.

It’s important to note that, for the FDA-approved treatment options, safety and efficacy have been demonstrated when the products are used as directed.

Over the counter, FDA-approved treatments

Over the counter treatments for lice, like Nix and RID, contain either pyrethroids or pyrethrins. Pyrethroids are the synthetic version of the natural pyrethrins, which are produced by chrysanthemums. These are the only brands I knew about during the aforementioned Great Delousing of 2014. Most of the human health concerns about pyrethrins and pyrethroids are related to occupational exposure in agriculture and ingestion. The primary mode of contact for lice treatments is through the skin.

Pyrethrins and pyrethroids are absorbed poorly through the skin so the risk is low for lice treatments. They can be skin irritants and may cause tingling and numbness at the site of contact. People who are allergic to chrysanthemums should avoid pyrethrins. Inhalation can also be a concern (although this data comes from using foggers to apply these pesticides agriculturally) so it is a good idea to use these treatments in a well-ventilated room.

Some lice are resistant to these pesticides as discussed in the AAP report on Head Lice. In addition, these treatments don’t kill the eggs and require retreatment for up to 10 days to fully remove all the eggs.

FDA-approved Prescription Treatments

Spinosad is a natural insecticide produced by a soil bacteria. Natroba (active ingredient: spinosad) was approved by the FDA for the treatment of head lice in people in 2011 and is available by prescription only. This approval is strictly for people over the age of 4, since safety in children younger than 4 has not been established. The FDA approval explicitly states that Natroba should not be used in infants because it contains benzyl alcohol, which can have serious adverse reactions in infants.

A major advantage of Spinosad is both pediculicidal and ovicidal (it kills both the nits and the adult bugs) so it requires only one treatment. The most adverse effect is that spinosad can cause irritation and redness if it gets in your eyes or on your skin, but these are rare (1-3%). Like pyrethrins and pyrethroids, spinosad is poorly absorbed through the skin so the risk of exposure from lice treatments is small. Based on this, the risks to human health from dermal exposure are even lower than the risks for ingesting it. Even by ingestion, the toxicity of spinosad is very low.

Ivermectin is actually an anti-parasitic agent that is on the World Health Organization’s List of Essential Medicines because it treats parasitic diseases found in many developing countries. It was approved by the FDA in 2012 for treating head lice in kids 6 months and older. Unlike spinosad, ivermectin kills larvae but not the eggs. Instead, it prevents newly hatched larvae from surviving, so it works better than the OTC treatments, but not at as well as spinosad. While there is toxicity associated with ingestion of ivermectin, there are no significant toxicity concerns with dermal exposure to ivermectin (especially when used only once or twice to treat lice). Like spinosad, adverse events include skin and eye irritation, but are rare.

Two treatments that are not generally recommended anymore are lindane and malathion. Lindane is an organochlorine pesticide that is no longer recommended by the American Academy of Pediatrics as a first line treatment against lice, due to concern about side effects. Malathion has one of the highest cure rates with a single application but has been removed from the market multiple times because of issues with application time, flammability, and odor.

“Natural” remedies

Essential oils

Many companies make claims about using essential oils for lice removal, but few studies have been done on effectiveness. There is very high variability in the makeup of essential oils so it’s also hard to say exactly what you are getting in any given product. Many essential oils have a high likelihood of skin irritation and many contain endocrine disrupting chemicals. Because these are “natural” products, they don’t have to meet the same FDA standards that the treatments described above need to. This also means that there are very few studies on whether these work and what the adverse effects might be. Because of the lack of data on these products, the AAP specifically cautions against using the products on infants and children.

Occlusive treatments

These are treatments that are applied to suffocate the lice. Some home remedies fall into this category: mayonnaise, butter, margarine, or various types of oils. There is limited evidence on these and they have not been studied at all.

Dimethicone is commonly used in OTC products as an occlusive agent. It is a silicone oil that by suffocating the lice. Because it only kills the bugs, but not the nits, retreatment or use in combination with the nit comb is required. It is not FDA approved for the treatment of lice; it is not listed on the CDC’s recommended treatments for head lice. However, there are a handful of studies that indicate that some products with dimethicone may be quite effective when used in conjunction with careful combing (some of these studies did not compare to combing only).

Let’s also get some semantics out of the way. Dimethicone containing products are often advertised in “chemical-free” or “pesticide-free” lice treatments. This is deliberately misleading. Dimethicone is a chemical. It also is technically a pesticide in this case: pesticides kills pests and it is being used to kill pests. Calling it “pesticide-free” is all marketing. It just has a different mechanism of killing lice. Those labels sound nice but don’t tell us anything about safety and efficacy.

Dessication

There is a company that sells a very expensive, hyped up hair dryer that is supposed to kill both eggs and bugs by blasting them with hot air for 30 minutes. This requires special training to use. There is only one study of this but results were potentially promising. A normal hair dryer should never be used since it can blow lice around and spread them.

Manual removal

This was our solution in the Great Delousing of 2014, since most other treatments required multiple sessions of combing anyway. These combs can be used on their own or in conjunction with other treatments. As a service, this option can cost multiple hundreds of dollars, but at home it involves a one-time purchase of a $10 comb. There are some products that claim to loosen the sticky substance that helps nits and lice stick to the hair, but these are also very harsh on the hair, don’t seem to be effective in clinical trials, and can interfere with some of the other products (pyrethroids, in particular). We used a regular detangling spray to make combing easier.

Economic considerations

While we’ve reviewed some common remedies here, the decision of how to treat your child’s lice is not only about what the science says. There are often economic considerations. Some of these options are more expensive, some require a prescription and may be pricey if your health insurance doesn’t cover it.

Some schools and camps have “no-nit” policies, even though the American Academy of Pediatrics (AAP) and the National Association of School Nurses (NASN) both recommend that these policies be discontinued, so people who can’t afford to take time off of work may need to factor that into their decision.

If this is a consideration, you may want to choose something that kills the eggs and the bugs as well (like Spinosad) and not something that takes multiple applications over 2 weeks (like dimethicone-, pyrethrin- or pyrethroid-containing products). Using something that is only effective half the time may also not be an option if you can’t stay home with your child until they are cleared.

Don’t forget that you also have to clean ALL THE STUFF. According to the CDC:

“hats, scarves, pillow cases, bedding, clothing, and towels worn or used by the infested person in the 2-day period just before treatment is started can be machine washed and dried using the hot water and hot air cycles because lice and eggs are killed by exposure for 5 minutes to temperatures greater than 53.5°C (128.3°F). Items that cannot be laundered may be dry-cleaned or sealed in a plastic bag for two weeks. Items such as hats, grooming aids, and towels that come in contact with the hair of an infested person should not be shared. Vacuuming furniture and floors can remove an infested person’s hairs that might have viable nits attached.”

Lice are not a sign of poor hygiene and they are also not harmful. They do not carry or spread disease.

Further reading

Edited 7/17/18 to add information about CDC recommendations about no-nit policies.