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