What’s the best way to repel mosquitoes?

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Do a Google search on this phrase, and I’m afraid nearly all the top results will try to sell you garbage. You can buy solar-powered ultrasound “repellers” that claim to scare mosquitoes off–but they’ll mostly just make your hamsters go crazy.

You can get patchouli and clove oils that say they repel mozzies–but they really just make you smell like a hippie.

This post will help you choose the right repellent, based on current research. You need to be a skeptical and careful consumer, because making a mistake can have serious consequences! Some of the deadliest diseases on earth are transmitted by mosquitoes.

How do mosquitoes find me, anyway?

I don’t know about you, but I’m a mosquito magnet. Other people safe from mosquitoescan be outside with me, but I’m the one in the big cloud of bugs. A huge amount of variability exists between the “attractiveness” of different people (to mosquitoes). Several different compounds on your skin help mosquitoes track you down, but their main tracking device is CO2. Unless you’re a zombie, not breathing is generally impossible as a mosquito avoidance strategy.**

What does work to repel insects?

A variety of chemicals repel mosquitoes. However, you need to choose carefully and with some attention to detail. Let’s start with just lotions and sprays, to keep things simple. (I’ll cover some other methods in another post).
You want to find out:

  1. What’s the active ingredient? Is it one that’s been shown to be effective?
  2. What’s the concentration of the active ingredient? Is it the amount (or percentage) that’s been shown effective?
  3. What kind of formulation is it? In other words, how does the active ingredient get on your skin?
  4. Does the active ingredient work to repel other biting insects and ticks?

DEET

The “gold standard” active ingredient is DEET, or N, N diethyl-m-toluamide. This has been on the market for 50 years, and the number of adverse reactions have been remarkably small for such a long time period. (And most were from people who grossly misused it–DEET is not meant to be used internally!)

It is universally acknowledged as THE best repellent around, and has broad repellent activity against several types of biting flies and ticks.

ChartHowever, when you go to your grocery store, you’ll be presented with a huge number of choices of just DEET products. You can get a “Skintastic” formulation that is 6% DEET; you can get “Deep Woods” formulation that is 30% DEET; you can get wristbands with DEET in them, and multiple brands. What should you choose?

If you look at the chart, you’ll quickly see that the wrist bands are worthless. (That’s the “formulation” part.) The very low dose DEET products protect for less time than the longer doses–about an hour and a half, compared to 5 hours of protection at the high dose. So, if you are going to be outside for short periods of time, a lower dose might be just fine. If you are going to be outside longer and use a low dose, you’ll need to remember to reapply it regularly.

If you know that there is mosquito-carried disease in your area, I’d be extra careful and use a higher dose. You don’t have to drench yourself with the stuff–just cover all your exposed parts. I also spray my clothes, since I’ve found the more aggressive mosquitoes will bite right through the seat of my pants!

You can buy up to 100% DEET products, but you don’t need to–research suggests that anything above 45% DEET doesn’t really increase protection.

Many people are concerned about DEET use on kids–the American Association of Pediatricians has a statement about what’s safe: up to 30% is OK after 2 months of age. If you’re putting repellent on a kid, apply DEET to your own hands and then rub it on your rugrat. Don’t put DEET, or other repellents, on children’s hands. (You know everything goes in a kid’s mouth.)

What about natural herbal ingredients?

As I said in another post, burn all the citronella candles you want–you’ll just get the bugs in the mood. (Playing some Barry White might also be helpful.) Citronella lotion is equally useless.

Avon Skin-so-Soft in it’s original formulation also doesn’t work. While Soybean oil looks OK in the chart above, it’s been consistently effective for only about an hour and a half in most field trials. Additionally, it does not protect against ticks.

Generally, NO herbal oils have consistently performed well in field trials (mint, lemon grass, sandalwood, pennyroyal, catnip, garlic, etc.) unless they were at 100% concentration. That’s pretty darn expensive, and goopy to boot. There is little or no consistent data about these compounds’ effect on ticks or deerflies, the other biting menaces.

Because of the variability in human attractiveness (to mosquitoes!), some lucky few can slather themselves with these herbal lotions, and not be bitten. For the majority of us, that won’t work.

Additionally, you don’t want to just reduce the number of bites–you want to stop biting completely. That’s the only way to keep yourself safe from diseases. To completely prevent biting, you’re back to DEET, or one of the two compounds I’ll discuss below.

DEET Alternatives that do work

Several new compounds have been approved as alternatives to DEET, and do seem to work. The two new players are Picaridin (Bayrepel) and something with the catchy name of IR3535. Here again, concentration is key!

Most research on Picaridin is based on a 10% lotion and a 20% spray concentration. In those concentrations, Picaridin performs just as well as DEET, with long lasting repellency. Yay!

HOWEVER: These formulations are only available outside the US. Inside the US, what we have available is a 5% lotion, and a 10% spray. As you might expect, the protection time is about half (about 1-2 hrs.). So, if you use Picaridin in the US, you’ll need to re-apply it more often for full protection. Once Picaridin has been on the market a while, it will presumably get approval for a higher dosage from the EPA.

IR3535 is only available in a new formulation of Avon’s “Skin-so-Soft Plus IR3535″ in the US. (Note this is Not the same as regular Skin so Soft!) IR3535 has been sold in Europe for about 20 years. At this time, the data on it’s effectiveness is mixed. In some tests, it performs very well, on others–little or no protection. This suggests that an element of personal attractiveness is at work, and that depending on how much of a mosquito magnet you are, it may or may not work for you. I would use this with caution, or not at all.

In Conclusion:

Ultimately, you make the decision about what works best for you. But do consider the evidence when making that decision. :)

I’ll follow up on this post next week with info on some of the devices you can buy that claim to repel mosquitoes, and clothing with repellents in the fabric. Please always use repellents safely. Note that I’m not endorsing any specific products, assume no liability, yadda yadda yadda etc.

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**While joining the undead is a solution to the mosquito problem, it does have some other associated costs, most notably the constant search for brains and increased body maintenance needs.

Some References:

  • A great NEJM article (source of the table)
  • An updated version of the repellent comparison table, including Picaridin and IR3535
  • Picaridin: a new insect repellent. Journal of Drugs in Dermatology, Jan-Feb, 2004
  • Am. J. Trop. Med. Hyg., 59(2), 1998, pp. 323-324. Short Report: the safety and toxicity of insect repellents.
  • J Toxicol Clin Toxicol. 2003;41:831-9. DEET: a review and update of safety and risk in the general population.
  • Parasitol. Res. 101 (1): 169-177 2007. Field evaluation of the efficacy of proprietary repellent formulations with IR3535(R) and Picaridin against Aedes aegypti.
  • Phytother Res 19 (4): 303-9 Apr 2005. Comparative repellency of 38 essential oils against mosquito bites.

7 thoughts on “What’s the best way to repel mosquitoes?

  1. Phantom Midge

    And the new slogan for Picaridin: “Repel Insects? Make it So!”
    OK, that was lame…sorry ;-)

    Yeah, I’m looking forward to your discussion on the clothing impregnated with DEET. It it pretty high priced to be effective for a limited time…

  2. Huh. Just to make things more confusing, you can also get “Skin so Soft with Picaridin.”

    Basically, Avon is using the buzz (ha!) from the earlier ineffective lotion to market two new lotions with active ingredients. Smart.

  3. When I was spending hours-days-weeks-months out in the field, I had to wear a much-faded fedora, bandanna, long-sleeve shirt, gloves with the fingertips cut off, long pants, heavy socks and hiking boots. This was hell when it was 40°C / 104°F, but I’m one of those freckle-and-burn people. The good part was that in addition to blocking the UV, it provided an extra barrier between me and the arthropods, aside from that three-week period of July when there was some kind of annoying micro-Diptera that had a passion for orbiting my ears and face (I ended up wearing my net over my head), and of course, the inevitable chiggers that apparently have transporter devices to beam right through layers of garments to lodge underneath my underwear.

    I sprayed my clothes and hat with DEET, which meant I would end up with about four rambling ticks per day, rather than forty (that unfortunate data resulted from a couple days when I forgot to fog my garments). I only ended up with a couple attached, but it doesn’t take much — the second summer I was laid abed under my doctor’s care for Mono AND Lyme. I’d never felt so exhausted and achey in my life; taking a shower required a nap afterwards. That prevented me from collecting that season’s field data and completing my 3rd & 4th stats classes (for some reason I kept falling asleep in class and couldn’t focus even when my eyes were open).

    As much as I would prefer a nicer-smelling, possibly less toxic herbal preparation, there’s no way I would trust anything not rigorously proven!

  4. I’m a mosquito magnet too. They never bothered my husband until we tried birding in Texas… those huge mosquitoes had him putting on Deet when he never had before! On the other hand, I never get chiggers and gets them a lot.

    I’ve noticed that some people who claim that mosquitoes never bother them DO get bitten… but whatever the mosquitoes inject that make other people itch just doesn’t affect them.

    I make Citronella/Lemon Eucalyptus soap because so many people asked for it… It doesn’t do anything for me but some people swear it works for them.

    Those natural oils you mentioned are not at all safe on the skin at 100%.

  5. Yeah, I thought that too. peppermint can be pretty irritating at high doses, as is eucalyptus.

    Well, at least your customers will smell good as they scratch their bites :)

  6. Emma Saunders

    Hey Guys,

    I’m currently in Vietnam and i’m using a lotion and spray with 50% deet in it and it’s not even touching the sides. I’ve been bitten big time regardless of all lotions. Any idea’s !? It’s so annoying and my legs look terrible!!

    Emma

  7. In a country with so much standing water, that’s a challenge. The first thing I’d suggest is wearing pants and long sleeved shirts, ideally ones treated with repellent.
    (I actually have a post in the works about mosquito repellent clothing–one well known brand is Buzz-off.)

    I know it’s hot, but this is the best way to be protected.

    You might also want to consider *other* biting insects are the problem–including bed bugs.

    What kinds of things are you doing there? (urban, rural, working with animals, etc?)

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