Do OTC Head Louse Treatments Work? Part 1: Mechanisms

I think it’s safe to say that most folks have had experiences with lice. Every entomologist I’ve ever met (including myself… buy me a few beers and I’ll tell you) has at least one entertaining pubic louse story. Head lice are a childhood rite of passage, with most kids being infested at one point or another. They’re generally harmless with the occasional secondary infection, but infested kids are prone to teasing and other forms of exclusion by classmates. Distraction due to constant itching can also be a problem. Since schools don’t want children being infested for obvious reasons, kids are sent home because of infestation, resulting in parents missing work. Even though lice are mainly nuisance pests, they’re still a pretty big economic pest and account for billions of dollars per year in lost productivity.

When lice strike

"We all have lice" by Antonia Hayes via Flickr.

Head lice are something almost everyone has to deal with, and head lice treatments are something someone buys every once and awhile. These are big business in and of themselves. Because they’re big business, many firms have started popping up offering louse treatments with varying degrees of effectiveness.

A while back, I went through my own head louse ordeal with my daughter. Treatment was complicated by a family member who didn’t realize they were infested. We originally thought the lice were resistant to treatment, so I had to get a second treatment. Since then, I’ve become curious about what is for sale in stores for Over The Counter (OTC) head louse treatments and generally take a look at whatever treatments I can when I get the chance. Over the years, I’ve become surprised at how many dubious treatments are offered for sale (although perhaps I shouldn’t be) and how many of these use questionable advertising techniques mostly built upon fear rather than science. Many treatments offered for sale over the counter are either unproven, or have been proven not to work.

First, let’s discuss some headlouse biology. Then, let’s discuss how the treatments currently FDA approved work. In Do OTC Head Louse Treatments Work? Part 2: Questionable treatments, I’ll discuss the dubious treatments.

Disclaimer: I have worked in entry level positions at companies which sell these products. This, has not influenced my position. I should also mention that I’m not a medical professional and will not be discussing side-effects or risk-benefit analysis. I am an entomology graduate student who studies insect physiology and although I’ll mention the side effects of these products in passing I will not discuss them in detail. This post will discuss the science behind head louse therapies, how they work, and why some aren’t thought to work. I’ll also discuss the evidence that would be required to show that they work. This post deals with insect physiology and should not be mistaken for medical advice. Always consult a doctor if you think you may have health issues because blogs are notoriously bad places for medical advice*.

Lice biology

Male head louse, via Wikipedia.

Head lice are small hemimetabolous insects – basically booklice that have evolved to be parasitic. They start life as an egg or nit attached to hair, then go through a series of nymphal stages before maturing to an adult.  The adults and nymphs both feed, injecting saliva that causes small localized immune reactions which is why you itch. They’re very well adapted to hair and grasp it with clawlike legs. They can only grasp onto some kinds of hair which is why you don’t get pubic lice and head lice occurring on the same body parts. They spend all their lives on hair, even staying on the hair while they feed. Actually, off hair (or similar

fibrous material) human lice are nearly useless and have trouble getting around. They must feed every few hours, otherwise they quickly starve to death or die of dehydration off the host. Lice are transmitted mainly through direct hair to hair contact, with objects like combs and hats playing a potential minor role in transmission.

The nervous system of head lice is surprisingly similar to ours, with differences that are minor as far as we’re concerned. The nervous system is composed of several thousand cooperating neurons and is involved with every aspect of a louse’s life, movement, feeding and reproduction and many products target this system. When a nerve fires, sodium and potassium channels open which causes potassium to flow out of the cell and sodium to flow back in. Often, this process is touched off by the binding of another messenger such as acetylcholine which causes these channels to open. The charge changes from a negative charge to a positive charge, known as depolarization. The positive charge is very localized and moves down the nerve cell as a result of the sodium/potassium channels opening and closing in a very tightly regulated sequence that is essential to function. Other channels can prevent the nerves from firing such as GABA which binds to a receptor and causes the opening of chloride channels which prevent the nerve cell from firing by causing it to attain a very negative electrical charge. The pesticides used in headlouse treatments target all these systems, all of which can lead to a dysregulation of the nervous system and a collapse of nervous system function.

How do louse treatments work?

The safest products are sold over the counter and are used as commonly available first line treatments. Pyrethroids are generally considered to be the least toxic product, and are the most widely available. Lindane is a bit more toxic than either pyrethrum or malathion but most adverse reactions are still due to misuse. All three of these pesticides target different systems in the louse. Resistance has been documented in lindane and pyrethroid insecticides, but not malathion in the US. Pyrethroid based insecticides are used as a first line of attack with lindane and malathion being listed as a second and third route of attack respectively due to resistance of lindane and lack of resistance to malathion.

Pyrethroids are compounds similar to pyrethrum which is derived from the chrysanthemum plant.

Chemical structure of pyrethrum, the most commonly used pyrethroid derived from chrysanthemum plants.

Pyrethrum is a botanical product, while pyrethrins are artificial versions of this compound which have varying degrees of effectiveness on insects. In general, the artificial versions are more toxic to insects and less toxic to mammals based on LD50 values. Pyrethrum is the compound used in head lice treatments. Pyrethrum acts by propping open the sodium channels, allowing a sodium influx into the nerve cells. The nerve cells then become depolarized in unison, which results in the discoordination of the nervous system. The nervous system eventually shuts down, followed by the louse’s vital systems.

Resistance to this pesticide exists in two forms, knockdown resistance and cytochrome p450 degredation. Cytochrome p450s are enzymes which detoxify various compounds and catalyze a wide variety of breakdown reactions. These enzymes are present in humans as well, and also serve to detoxify the small amount of pyrethroids which are absorbed during treatment. In many resistant strains, the cytochrome p450s are upregulated, or overproduced. The overproduction of specific cytochrome p450 enzymes results in the increased breakdown of the pesticide. To combat this, a common additive called piperonyl butoxide is added as a cytp450 inhibitor. Knockdown resistance occurswith a change in the sodium channel that decreases the sensitivity to the pyrethrum, which is more difficult to combat. This is a wonderful example of evolution in action because it’s something which has evolved in direct response to usage of pyrethroids in headlouse treatment.

Chemical structure of lindane, courtesy of wikipedia commons. The molecule consists of a 6 membered ring decorated with chlorine atoms.

Lindane acts by binding to the GABA receptor and permanently inhibiting it. This results in the influx of chloride ions. With the GABA receptor stuck to the ‘on’ position, the nerves are unable to transmit any signals. This  mechanism is semi-complex mechanism but briefly the chloride ions reduce the charge in the cells, so much so that when the potassium flows out the nerve cell is still negatively charged and never fires. The nerves are unable to fire, and are in effect turned off. With the nervous system turned off, the louse becomes permanently paralyzed and dies as a result of not being able to feed. Resistance has been documented to lindane, but I’m not sure what the mechanism is. This product is one of the more toxic substances on the market for head louse treatment, and generally isn’t prescribed for children.

A third mechanism revolves around acetylcholinesterase, an enzyme not directly involved in the transmission of nerve signals. Acetylcholine Is used as a neurotransmitter, being sent between nerve cells to cause them to fire. When an action potential reaches the end of a nerve cell, the nerve cell releases acetylcholine which results in the nerve cell firing. Acetylcholine is degraded by an enzyme called acetylcholinesterase. Without acetylcholinesterase, the nerve remains permanently depolarized and the ion gradients collapse.

Chemical structure of malathion. The active portion of the molecule is the phosphate-like group on the far left which modifies the place in the enzyme responsible for catalyzing the reaction which shuts off nerve cells temporarily.

Even though acetylcholinesterase isn’t directly involved in the transmission of the signal, the enzyme is still important in ensuring the proper working of the nervous system. Organophosphates such as malathion knock the enzyme out, killing the insects. Malathion is an interesting molecule in and of itself. Toxicity requires degredation to another product, which happens better in insects than in mammals. Malathion is sold in a solution that contains isopropyl alcohol and tea tree oil which both synergize the effects of malathion by mechanisms which aren’t well understood. They work either by denaturing protiens in the lice as in isopropyl alcohol or by acting as a supplementary antiacetylcholinesterase as in tea tree oil.

Another method which has been used to cure head lice is what I refer to as the ‘nuclear option’ (or, to use a rare euphemism… landscaping for crab lice), and that’s simply removing the child’s hair. Without hair, the lice cannot hold onto their host and simply fall off. While side effects of the above treatments are relatively rare when the pesticide is used properly, this is by far the safest and most effective method of louse control. Unfortunately, this may not be acceptable for many people. When my daughter had head lice, she did not want to have her head shaved and this is the case for many little girls.

Are there treatment risks?

Although I’m keeping this post focused mainly on the mechanisms of these pesticides, remember that it’s the dose which makes the poison and any substance can be toxic when given in a high enough dose. Exposing yourself to a small amount of pesticide is OK so long as you allow it to break down and leave your system. Repeated exposure over a very long period isn’t a good thing because these products do inhibit neuronal function, leaving the door open for possible neurodevelopmental effects. Because of this, these products are not reccomended for long term use and treatment regimens are designed to last as short as possible. Head lice generally take about ten days to two weeks to mature into adults which is why retreatment is recommended within a week. Many products (except lindane) do not kill eggs, so any leftover eggs will hatch and eventually grow to reproductive adults if a followup treatment isn’t performed. The active ingredients have proven useful in a variety of contexts, including agriculture, but in this case the trick is to treat the patient with a dose high enough to kill most of the lice but low enough to not cause symptoms in the human.

Classifying these chemicals as pesticides sounds scary to many, and many companies have figured out how to take advantage of the unease many parents feel about treating their kids to sell products which have no evidence of efficacy. Next week, I’m going to expose many of these products and further explain the science behind clinical trials for these products.

* One of my favorite fellow entomobloggers, Bug Girl, even has a page titled ‘I will not diagnose you’ and this applies to me as well. Do not contact me asking for any diagnosis because any E-mails of this character will be sent directly to my junk E-mail folder as it is outside of my duties as an entomologist to perform this sort of work and would be completely irresponsible.

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Joe Ballenger is an entomologist who works in the biotech industry as a contractor. In his spare time, he helps answer questions about bugs at Ask an Entomologist.

  • jerry

    Great article one of the best explanations of the activity of the pesticides I have come across.

  • terry

    Good article, but it might be worth pointing out that some people are low in the enzyme PON1 which is needed to clear organophosphates like Malathion from the body. The organophosphate pesticides that we use today (OPs) are derived from the nerve gases developed by I G Farben in Germany in the 1930s for military use, in a dilute form. Without the enzymes to clear OPs from the body, repeated use may cause problems.

  • Jen

    This is fantastic. I cannot WAIT to read Part 2, I’ve been digging for accurate information around this for months. I’m so glad you’re doing this.

  • To equate organophosphate pesticides with nerve gasses is a bit misleading. We don’t spray sarin or VX on crop plots because they’re simply too dangerous to use. Modern organophosphate insecticides are designed to be somewhat selective to insects.

    It’s possible that PON1 deficiency could cause problems, but the entirety of the work that’s been done in the scientific literature has been on long term effects in agricultural workers and their families. Agricultural workers are exposed to this stuff on a nearly constant basis, and head louse treatments are designed to be used only a couple times during the life of the individual. The studies should still be done, but there’s quite a bit of difference between the doses the family of agricultural workers are exposed to and the doses given in head louse treatments.

    I’ve always wanted to do a post on insecticide selectivity, because it’s an interesting area of research that actually incorporates evolution and biochemistry to produce a useful product. I was at a conference not too long ago where they were talking about the evolution of acetylcholinesterase genes, the shape of their active sites and how this affected the toxicity of pesticides. It’s truly fascinating stuff, but I’ve got a lot on my plate right now and I’ll probably be pushing it off for awhile yet.

    Pesticides, especially OPs, are nothing to take lightly, but aren’t nearly as evil as many would lead you to believe.

    • I’d love to learn more about insecticide selectivity. In particular I think the story of pythrethroids is interesting. From what I know about it, humans took a naturally occurring insecticide found in plants and were able to create synthetic versions that are safer and more selective. What a success story for modern chemistry.

  • I own a head lice treatment center. The majority of my clients have used OTC products with no success. They still have live bugs when they come in. I use an enzyme with no pesticide to kill lice. But nothing kills the eggs so the proper nit comb is required. Everyone concentrates on the product that will eliminate this problem when in fact it is the proper comb that will do the job. No product alone with rid you of this itchy problem. With that being said, why use chemicals when an enzyme with no chemicals works and is not dangerous. All of these OTC products should be removed from the shelves. They are worthless and the comb that comes with these products are a joke.

    • I don’t mean to pick on semantics here, but if your enzyme kills lice, isn’t by definition a pesticide? And, I don’t mean to be difficult, but enzymes most certainly chemicals.

      What characteristics of the comb that comes with OTC products make them “a joke”, and what about the combs you use is better?

      • Stop being a snarky know it all

        What makes the OTC combs a joke is that the the teeth are not tightly spaced enough to catch the nits. They literally go right over the nits and you can see the hair and egg pass through unscathed. The “Rid” comb could not even catch one nit on my child’s head because her hair is fine. I suppose it might work in coarse hair but most of the population has hair that is finer than the OTC comb teeth. The comb that works is very fine toothed and has ridges. The one I used that worked I purchased on Amazon because it had over 200+ positive reviews from grateful families who said it worked.

        And yes you were picking on semantics and being rudely snarky. The lady who owns the lice salon was just giving you the facts and you know darn well that by pesticide she was talking about the neurotoxins that are used in the OTC medications. By your estimation your fingernail is a pesticide as you can crush a bug. Try to be a little more down to earth – apparently you have no idea what a nightmare this is for families, schools and communities. The problem is exacerbated by the false sense of security families have when they are told the answer is nearby at the drugstore only to find after a lot of grief that the OTC treatments do not work! I went straight to my doctor and got the prescription pesticide and half the bugs and nits lived right through it. The OTC comb as said passed right over the ones left in the hair. I had to do a couple home remedies while waiting for the professional comb to come in the mail.

        • Thanks for assuming that I was being “rudely snarky”. In fact, I was just asking stating a fact and asking a question, putting it as politely as I could. Granted, you can’t hear tone of voice in a text comment, but here you assume the worst and you are being rather rude in response. I could respond to you rudely, but that’s not how I do things.

          I do appreciate your explanation of how combs from Amazon are superior to those in OTC products. Unfortunately, Carol simply said the OTC combs “are a joke” which really didn’t tell me much. Based on images of “Fairy Tales” and “Nix” combs on Amazon, it seems that the teeth spacing is similar, but it is hard to tell without a direct comparison. I’ll have to take your word for it at this time.

          What I was alluding to is the demonization of certain words to the point that their meanings are frequently confused.

          A quick dictionary look up: A pesticide is “a substance used to destroy pests”. Chemical has two meanings: 1) “of, relating to, used in, or produced by chemistry” and 2) “acting or operated or produced by chemicals”. Enzymes are “complex proteins that are produced by living cells and catalyze specific biochemical reactions at body temperatures”.

          Note that none of these words indicates anything about the “naturalness”, safety, or other details of the substance in question. So, yes, an enzyme, including the one Carol uses, most certainly is a pesticide and is a chemical. A fingernail is not a pesticide and neither is a comb. (also, see Joe’s response below)

          Words are important. When we have more and more goofiness like chemical-free chemistry sets and chemical-free sunscreen it is indeed important to point out what is and is not a chemical. When purveyors of organic products claim that organic means pesticide free (when what they really mean is synthetic pesticide free) it is indeed important to point out what is and is not a pesticide. Yes, some chemicals and some pesticides are harmful to people but not all chemicals and pesticides are harmful to people. Changing the pop-culture meaning of the words to be just “something that is harmful to people” means that people are now afraid whenever they hear chemical or pesticide.

          It is just semantics, as in “the branch of linguistics and logic concerned with meaning,” but that doesn’t mean that meaning isn’t important. Further, being concerned with the meaning of words is not mutually exclusive with caring about the hardship that people infected with lice have to endure – but thanks for assuming that I have zero empathy.

          Thankfully, I haven’t had lice since I was a child. I do not yet have children of my own. So, I do not have much personal experience beyond a not-too-fond remembrance of my mother having a very hard time removing nits from the very fine, very light blond hair of myself and my three siblings. The white eggs were impossible to see, so it took hours and hours. Despite this being quite a long time ago, I do vividly remember how how difficult and stressful the experience was for my family. I’d imagine that most people have at least one experience with lice.

          I can certainly empathize with families needing to find products that work, be it pesticides or combs. It is actually because I have empathy that I want people to be able to access science-based information about the products that they are considering using on themselves or their children – and that is exactly the point of Joe’s blog post.

        • I actually take offense to the assumption that anybody who questions a product’s effectiveness doesn’t care about people who are afflicted by the condition the product claims to treat. You’d think that someone who actually took the time to parse the claims of these manufacturers to see if their claims were on the up-and-up would care more about people afflicted with the condition than someone who took such claims at face value and didn’t ask such questions.

          And also, I very briefly shared my experiences with lice in the opening paragraph. I am a single parent, and my daughter dealt with a head louse infestation for quite awhile because of products like those mentioned in part 2. So…yes. I have personal experience with this, and I do care. Which is why I wrote the post.

          I know firsthand what a nightmare this is for communities and families because I have been through this and have personal experience. Furthermore, companies like TecLabs sponsor PTA meetings while selling products that are little more than diluted salt water that have not undergone clinical studies to prove their efficacy. In fact, I have a post coming up which does a very good job of questioning whether their product kills lice or if they’re interpreting immobile lice as dead. I think this is a *huge* problem, and evidently you should too based on what you said about OTC treatments not working. The legal loopholes I mention in Part 2 are a huge part of that problem.

          That being said, I honestly hadn’t considered whether mechanical instruments should be labeled as pesticides despite the fact they kill pests. It’s an interesting consideration. Truth be told, such devices are seldom used on a large scale. Besides louse combs and possibly flyswatters, I’m not aware of any purely mechanical devices which have been used to kill insects on a widespread scale since the invention of Benson’s Colorado Potato Beetle collector in 1866. Perhaps there are others, but I’m not aware of them.

          Despite this, the original context of my article and response was purely biochemical in nature and the definition fits in this context when applied to enzymes. I refer you to Anastasia’s post as well as my original post for my reasoning. Semantics, which is the meaning of words, are important for exactly the reason Anastasia said.

          Facts are built on data. Without data to support them, facts are only claims. Anybody can make up a claim. Lots of people can make claims. What makes them a fact is the quality of the data which supports them, and this is often difficult to parse. If there are no data to support a claim, the claim can be rejected until there’s data to support it. Once there’s data to support the claim, that data can be questioned because it’s easy to misinterpret the data. Heck, two people can read a study and have different interpretations of the data. However, once enough studies have been done the data becomes harder and harder to legitimately question and this is how ‘facts’ are born. Then, sometimes things change (e.g. pesticide resistance) and we’ve got to start all over again.

          …but the important thing is that you *have* to look at the data each step of the way. This is what I was doing, this is what the commenter failed to supply. Thus, I rejected her claim based on lack of evidence.

          Now since you’ve accused me of being arrogant, I want to ask you a question. Furthermore, I want a bluntly honest answer.

          In this article, part 2 and my forthcoming update I went to extreme lengths to make sure every claim I made was based on actual data. Furthermore, I put a great deal of effort into discussing the quality of the data I discussed to help readers decide if they agreed with me.

          If we define arrogance as an offensive display of superiority, self-importance or overbearing pride then who is more arrogant: the graduate student who openly displays and discusses the data behind his claims with no intention of making a profit, or the business owner who expects the world to take their claims at face value?

          What do you think? And why?

  • Actually, Anastasia, in this case semantics are pretty important and I make a huge deal about semantics in my next post. Most of science is definitions, and these definitions are important.

    By claiming a product kills lice you’re claiming it has pesticidal, insecticidal and pediculicidal activity. To claim that your pesticide free product kills lice is to essentially admit it either doesn’t kill lice or isn’t pesticide free. This is a contradiction of terms.

    Enzymes are made of atoms, have set compositions and generally can’t be broken down into simpler substances without breaking chemical bonds with the obvious exceptions of things like cytochrome p450s that use heme molecules as cofactors. This means that they are, in fact, chemicals because they fit the textbook definition.

    In short: Anastasia, you are exactly right. Anything which kills lice is a pesticide by definition, and enzymes are chemicals.

    The reason why most folks have problems with OTC treatments is that about half the stuff on the market is marketed in ways that allow them to skip safety and efficacy testing. Most, with the exceptions of the active ingredients listed in this post, don’t appear to have been tested on lice at all.

    It’s funny…these posts represent three years of on/off efforts of looking into the active ingredients of head louse products. I really didn’t know there were entire treatment centers which catered to lice removal. I was pretty caught up in looking at insecticidal data on plant extracts and the like that I didn’t even think to look for lice treatment businesses. I shall look into this further.

    Carol, I’m particularly interested in seeing the data behind the claims made about the products on your website. I’d very much like to know if you’ve published any work on this. If so, please give the citation below and I’ll look into things myself. In particular, these are the claims that interest me:

    Your claim that 99% of lice were killed by your shampoo. Were these in vivo tests? How, exactly was mortality assessed? At what time points post-treatment were the patients assessed?

    Your claims that your shampoos prevent reinfestation. How, exactly was this data gathered?

  • The OTC combs are either plastic or metal with the teeth too far apart for effective nit removal. Our comb has micro-grooving on each tooth and the teeth are very close together. It has been tested against the other combs on the market and has been proven to drag out the most lice and nits.

    I consider the OTC combs a joke because the majority of my clients have used these combs and they are still fully loaded with nits. I also sell my products for people to use themselves, those people are able to remove a lice infestation easily.

    My point about the enzymes is that it kills the lice cleanly and quickly without harm to humans. The OTC products contain pesticides that are harmful to humans. I have seen first-hand how children are taken to the hospital after using these products. The enzymes we use are hands down more effective and safer to use than lindane, malathion, etc.

    If you are interested in the the nit comb and enzyme study, please contact Katie Shepherd at Lice Solutions Research Network. She has a team of people who research lice and lice products. I get all of my information from her.

  • Jen

    I’ve done a lot of research on the growing head lice treatment industry and the products used, and have also been confused about enzymes. From what I understand, the claims are that enzymes dissolve the exoskeleton of the louse.

    I’ve also researched the combs, and think there was an evolution from the Nisska comb which is a stainless steel comb that is made in Germany and was being used by a group of women in NYC who treat lice using the Nisska comb, Pantene conditioner, some baking soda for grit to help pull out eggs, and a little rubbing alcohol thrown in for good measure here and there on the comb. Then the National Pediculosis Association came out with their “Licemeister” comb and campaign against pesticides–not sure if the Licemeister name is an odd homage to the German origins of the comb they were imitating? Then came the Nit Free Terminator Comb with “patented microgrooves”.

    For some of the OTC pesticide-free formulas, Nix PF looks to me to be based on a formula that was originally sold as Hair Clean 1-2-3 and I think may have originated in Israel using coconut oil, anise oil, ylang ylang oil and isporopyl alcohol–I’ve wondered if it’s the alcohol that would be the potential help in this. Lice MD is straight, 100% dimethicone which claims to suffocate the lice. Licefreee! gel lists sodium chloride as a pediculicide (?!) indicating that it dehydrates the lice.

    There is also the Lousebuster heated device which dries out the eggs, making them easier to comb. Among all of the other home remedies and oils and Listerine, etc.

    My personal conclusion for now based on what I know is that almost any product (conditioner, oil, foam) that you put on the head will slow live head lice down enough to comb them out, but that the only sure way to eliminate them is to keep combing until you make it through the reproductive cycle and then some so you catch any eggs that are missed in combing/picking.

    I do think the Terminator comb seems to be the most productive in pulling out lice. I haven’t tried the Nisska. So any product that makes combing easier and is safe enough seems to me the best complement to combing. I am eager to hear what you will have to say about this.

    On a separate note about enzymes–they seem to be making a big splash everywhere, including the health food/supplement industry claiming people are deficient in them, use in pond cleaning and environmental clean up, housecleaning, pet accident cleaning, even to improving pet odors when taken internally–I am not a scientist and have had a hard time figuring out exactly what enzymes are (and aren’t). So I hope as busy as you are that this might be addressed in part, at least as it relates to head lice. Thanks!

    • I actually do have a small confession to make. I’ve never actually looked into lice combs. The work I do is basically biochemistry work, which is why my interest in lice concerns the pesticides used to kill them. I’m sure there’s a bunch of important research on lice combs, but it’s stuff which hasn’t piqued my interest as much as the shampoos.

      Allow me to answer at least some of your questions here. I wrote part 2 as more of a piece intended to show the types of marketing techniques head lice products that don’t work use to promote themselves. There’s no way I could go through them all in detail, and each post is pretty time consuming in terms of the amount of stuff I read. If you look at the treatments and shampoos offered for sale by the Shepherd institue (first two hyperlinks at the bottom), many do not claim to kill lice and few actually show the pesticidal ingredients, although I do discuss X-pel in part 2. If the shampoo doesn’t show it’s ingredients and what concentration they’re in then there’s no way I can actually say whether or not they work. In the absence of evidence of efficacy (or in the absence of claims that the shampoos kill lice), I would assume the products do not work.

      I did run across dimethicone, but don’t remember much about the literature off the top of my head. I mentioned it in part 2 but didn’t discuss it in detail. There are papers which say this compound is effective at killing lice, but the timepoints surveyed are scattershot. I’m also pretty certian that the cure rates are lower than other pesticides. If you want, post in the next thread after the third and I’ll dig the literature back up.

      Enzymes are really nothing more than biomolecules that catalyze reactions. The enzymes I work with, for example, cleave phosphate groups off proteins and turn them off and on at inappropriate times. Saying something contains an ‘enzyme’ doesn’t really say much. Enzymes can cut proteins, fold proteins, build things, transfer parts of cells, tear stuff apart or even transport things across cell walls. Enzymes are the workhorses of biochemistry, and this is an area where there’s a lot of different jobs to do!

      I’ve seen some products that claimed to use enzymes, but didn’t think much of them for this reason. The exoskeleton of the louse is made of chitin coated in wax, which is pretty tough stuff and very difficult to dissolve. I’ve seen some combing aids that claim to dissolve the nit sheath which fastens the egg to the hair strand. I don’t believe these claims because the nit sheath is pretty close to keratin (third and fourth hyperlinks), which means that any protease that would dissolve this sheath would also dissolve hair.

      As for other products, it’s difficult to say. The washing detergent I use claims to have enzymes added, but it also pretty obviously contains a bunch of detergent. Detergent denatures proteins and stops their activity by destroying their structure, not unlike uncrumpling a ball of string. The enzymes in this formula are probably just useless bits of proteins floating around in solution unless they manage to recrumple themselves. This is possible, but unlikely. Either way, the detergent’s cheap so I’m probably not paying for their claim.

      There are pretreatments that aren’t detergent based that work quite well. It’s possible that these products use enzymes to break apart things, because the fibers that make up your shirt are pretty hard to cut. I don’t know this for certain, because I’ve never looked into it.

      I hope this answers your questions. Read part 2, which will be posted soonish, and post more questions. I’d love to answer more.


  • I looked up some of the dimeticone literature on a whim, and it looks like the literature on this product is riddled with missing controls and inadequate time points, throwing the efficacy of the product into question. I knew there was something funny about it, but I couldn’t remember what.

  • Jen

    Thank you for the information on enzymes, and on dimethicone.

    I can imagine you’d have no reason to look into lice combs–I only mentioned them as an aside. Also as I think some of the media attention around the pesticidal ingredients in OTC products may have come in large part from the efforts of the National Pediculosis Association and the marketing of their comb.

    The ingredients in the enzyme formulas used in many of the products used by lice treatment centers are listed as: “naturally occurring, non-bacterial, readily biodegradable, enzymatic solution derived from safe yeast strains, water, mild non-ionic surfactant blend.”

    I’ve been trying to understand what the ingredients in these formulations imply for a while–is it the surfactant blend that would actually provide any potential activity? I know I have enzymes in my saliva so if I spit in a cup of water is that going to be significantly different than enzymes from “safe yeast strains”?

    I’m looking forward to reading your second post, and about X-Pel which I’ve also tried to figure out (homeopathic? bee pollen?) and anything else you may say really. I also agree with you and Anastasia in that semantics are important and would like to know what your take on the marketing terms used with these products will be.

  • the bug guy

    Jen, enzymes are basically proteins that mediate chemical reactions. In other words, biological catalysts. All living organisms produce these in large numbers. Some are similar between species and other very different.

    Trying to parse the product description you provided:

    naturally occurring, non-bacterial, readily biodegradable, enzymatic solution derived from safe yeast strains

    Lots of redundancy here. Materials derived from yeast are, by definition, non-bacterial. Also, enzymes and proteins extracts from living organisms are also, by definition, naturally occurring and almost always biodegradable. “Enzymatic solution” and “safe yeast strains” are non-descriptions in that they give no real information about the ingredients.


    Straightforward, but probably redundant since both other ingredients are solutions that, since no other solvents are noted, are likely water-based.

    mild non-ionic surfactant blend

    Essentially, a mild soap of unspecified chemistry. Mild surfactants are used to control other insects (insecticidal soaps), but I am not familiar with the research with lice as the target organism.

  • Jen

    So are mild surfactants used as a vehicle to deliver pesticides when used against insects, or are they also insecticides? From what I’ve read, some surfactants are considered toxic. I realize that toxic is a relative term, but if a product claims to be non-toxic then I don’t know if a product containing a surfactant can accurately say that, unless perhaps it is in a small enough quantity to be considered negligible.

    There is an overlap in products used for controlling insects in gardening, etc. with products used for lice treatment–the frequent use of peppermint, neem (which I’ve seen listed as a natural insecticide next to nicotine and pyrethrum), tea tree oil, and other fatty oils.

    What I’ve struggled to figure out is if any products used against head lice are truly pesticidal (and if so, to what degree) and also what claims a product used to treat head lice can make as far as being pesticide-free and non-toxic. For example, products with neem oil often claim to be pesticide-free, but that wouldn’t seem to be accurate from what I understand.

    Look forward to your next post.

    • the bug guy

      So are mild surfactants used as a vehicle to deliver pesticides when used against insects, or are they also insecticides?

      They can be either. They can be directly used as insecticides (such as the Safer brand), which act by covering or entering the respiratory spiracles and causing suffocation.

      Surfactants are also used as “spreader-stickers” in agricultural mixes. They act by reducing the solution surface tension, allowing the solution to spread more evenly over a plant surface. The surfactants also help to overcome the water repellency of leaf surface waxes, also allowing better coverage and adhesion.

      From what I’ve read, some surfactants are considered toxic. I realize that toxic is a relative term, but if a product claims to be non-toxic then I don’t know if a product containing a surfactant can accurately say that, unless perhaps it is in a small enough quantity to be considered negligible.

      Anything can be toxic in sufficient doses, even water. In general usage, materials with low toxicity administered at well below active levels are called nontoxic. In a regulatory sense, EPA toxin class IV is considered “practically nontoxic” (III is slightly toxic, II is moderately toxic and I is highly toxic, with the levels defined at specific levels). You would need to see the MSDS data on a particular surfactant to understand the potential for toxicity it represents.

      What I’ve struggled to figure out is if any products used against head lice are truly pesticidal (and if so, to what degree) and also what claims a product used to treat head lice can make as far as being pesticide-free and non-toxic. For example, products with neem oil often claim to be pesticide-free, but that wouldn’t seem to be accurate from what I understand.

      If the material is killing or adversely affecting insects, then it is an insecticide (or pesticide, to use your term). Even if it is a natural extract like neem oil. If a product claims to be pesticide-free, then it either has no ingredients that will kill or act against the insects, or the company is not being accurate.

      In general, you will need to examine the proper pesticide label or MSDS to see the toxicity potential. Each material is different. And, don’t assume that a produce it less toxic because it is natural. For example, you mentioned nicotine, which is very toxic even though it is a natural plant extract. It is far more acutely toxic that most current restricted use pesticides (these are materials that require a license to purchase and apply)

      Unfortunately, these things can get complicated and that is where articles like Joe’s above can be very helpful.

    • Folks like Jen are what make blogging fun. Keep asking questions, and I’ll keep answering. A lot of this stuff is covered in part 2, which should be posted any day now. TBG made an excellent post about this above mine and I refer you to him but I’ll add some stuff to his post.

      I haven’t seen a lot of information on inert ingredients in louse shampoos, so I can really only speculate based off what I know about normal shampoo chemistry and insecticidal soaps used in organic agriculture. I’d imagine the two most likely surfactants used in these shampoos are either sodium dodecyl sulfate (SDS) or fatty acids derived from fats (KFAs). SDS is used in most shampoos and is safe in the amounts used in shampoos.

      KFAs are generally forumulated as potassium salts of breakdown products of fat (think Fight Club) and are normal metabolic byproducts. KFAs are also used as pesticides in organic agriculture to remove the wax layer on the outside of the insect which prevents dehydration, thus dehydrating the target insects.

      I doubt they have any significant insecticidal activity as lice can survive normal shampooing pretty easily.

  • the bug guy

    First paragraph in my reply to Jen should’ve been in blockquotes.

  • Jen

    Thanks, Bug Guy! I appreciate your answers, and the forum.

    I don’t think many of the oils (citronella, eucalyptus, rosemary, lemongrass, tea tree oil) are in OTC treatment formulations in the states, but they are a staple in alternative/home treatment remedies, and are now hitting retailers in repellant products (Lice Shield, etc.)

    It’s been hard for me to find clear facts about how effective any of these are in treatment or prevention, and how safe they are–along with the enzymes for treatment. But I realize this veers away from OTC treatments which was the initial focus of the article.

    Thank you!

    • Well, Jen the other purpose of forums like this is to give bloggers like me ideas to write about which is why I like to encourage questions like the ones you’re asking. I’m already considering doing a post about lice treatment clinics, because I think this adds some interesting nuances to the story. I agree with you that I should also do a post about home remedies. I try to be as thorough as I can, which is why my posts are generally pretty long.

      When I get to these posts all depends on how much I’ve got time to write in the coming weeks. I’m going to be teaching, taking classes and doing research again soon. All of this comes far before side projects like this.

      There are also other science-related things I’d like to discuss. There are another series of posts on here about genetically modified insects, and there have been some recent developments in that which I’d like to get to soon.

  • Jen

    Would be interested to see any/all of these posts. Genetically modified insects also!
    Good luck with the balancing the rest.

  • the bug guy

    You’re welcome, Jen.

    You mentioned several plant extracts/oils sold as repellents. That is a whole different area of active study. Different species have different responses to each of these chemicals, so it is very hard to make any broad statements about their effectiveness.

    Google Scholar is a good, freely available search database for academic literature. Access to the articles varies between publisher. For example, the Entomological Society of America papers are free online if the author requests it, while all of the published material from the Florida Entomological Society is available free online. If you have access to a university library, you can often use their online subscriptions to download the articles and either print on site or save as a pdf file.

  • Jen

    Thanks again, Bug Guy!

  • Bob

    I appreciate the information and discussion here.
    May I ask where to find detailed physiology and biochemistry data about head lice? I’m a scientifically literate non-entymologist who has been through a family louse infestation, and I have a simple de-lousing idea I want to look into. Any recommendations on the relevant books or journals would be most welcome. I’m particularly interested in the physiology and biochemistry of respiration and the control of respiration across the life cycle.

    • Bob, I’m sorry I took so long to see this post. I do my blogging during the summer months and during the winter months when I’m not teaching.

      What I would do is start by looking through review articles on pubmed. The titles and abstracts will help you figure out if this is in your vein of interest. Although many works are in the public domain, quite a few aren’t. If you find an article you’d really like to read, use the contact function here on BF to send me the author, year and title the article was written and I’ll try to send it to you as a PDF when I’ve got the time.

      The CDC also has great information on head louse treatment and biology. When I’m researching to teach a class, it’s usually the first place I go.

  • vandi

    thankyou for your wonderfully factual, thoughtful,info.and your time. i get frustrated trying to find facts about most things i look up online, so much is promotional, imaginary,or vague. often an array of conflicting answers, which leaves me where i was before i asked.(my family has lice right now,or, we hope not, but we’re in the process of de-bugging. so far, kids are in tents to avoid beds for a few days. boys are buzzed, my daughter and i have put some greasy dimethicone type stuff in our hair, and think it killed bugs, but didn’t loosen eggs. and the combs don’t work well. slide over most eggs. am considering neem oil. ) blah blah.. is worry on my mind! anyway, thanks.

  • I learned about a new lice treatment option with Spinosad as the active ingredient. It’s a protein produced by soil bacteria and from what I can tell, extremely safe. The website claims that you don’t have to comb nits, which sounds like a huge advantage over other treatments.
    I’d love to hear from anyone who has used this treatment.