The Buzzz on Mosquito Repellents
Finally! There’s an alternative to DEET that actually works.
Picaridin was developed by the German pharmaceutical giant Bayer in the eighties, has been used in Europe for years and was recently approved by the EPA as an insect repellent. It is marketed in the U.S. under the name Cutter Advanced.
Although it may sound like it should, (RS)-sec-butyl 2-(2-hydroxyethyl)piperidine-1-carboxylate (picaridin) doesn’t smell like a cross between the back of a drawer in a high school organic chemistry lab and an oil refinery. It’s nearly odorless and colorless, not oily and has only a vague flavor of dish soap.
The Field Tests
Concentration variants are now available for picaridin (from 7% – 24% solutions) and there are also a couple of alternate suppliers in the U.S. Cutter Advanced manufacturer United Industries Corp. was the only licensee but was recently joined by Natrapel by Tender Corp.
We compared the spray on with the disposable wipes and found the protection the same but the wipes easier to use especially to get complete coverage on children.
The tests were far from scientific but they convinced me. Six adults and three children (age 2-6) used Cutter Advance over six days of camping, biking, hiking and fishing and counted a total of nine bites at the end. Most were thought to be due to incomplete coverage or inadequate reapplication.
For a couple of days I used 95% DEET on my right side and picaridin on the left, but after zero bites on either side I switched to picaridin all over.
As a control I washed the repellent off my arms and torso and got three bites in about ten minutes.
A few things we noticed
- Picaridin lasts a much shorter time than a similar concentration of DEET. You need to reapply every 30-90 minutes. Subsequent applications seemed to last a bit longer (maybe an hour or two) so you might wait till the little buggers start hovering again.
- It seems to take more Picaridin than DEET to get the same area of skin covered. Perhaps this is because it’s not oily like DEET and doesn’t spread as well. In any case I’d recommend applying a little more generously at first and backing off as you get used to using it. As mentioned above the wipes were much easier for applying to kids.
- Wash your hands before eating. Picaridin doesn’t have much odor. I’ve always relied on the distinctive stench of DEET to remind me not to get my hands near my mouth or eyes.
- Water resistance whether from wading across streams or heavy sweat seemed reasonable.
What about Other Alternatives?
Mosquitoes have been my arch nemesis since I started hiking and camping forty odd years ago and I’ve tried every new repellent that’s come along. Avoiding bites is even more important in now with the introduction of the African diseases Chikungunya and Zika to Costa Rica’s mosquito population.
Until now there has only been one that worked for me –DEET (N, N-diethyl-m-toluamide).
In addition to repellents you can use insecticides to treat clothing (and tents, mosquito nets etc.) to aid in bite prevention. The most effective treatment for clothing that we’ve found is 0.5% Permethrin ((3 phenoxyphenyl) methyl 3-(2,2-dichloroethenyl) 2,2-dimethylcyclopropanecarboxylate) which seems to work quite well for about two weeks (and a couple of washings) after treatment.
Other Natural Repellents We’ve Tried
The only alternative we found that had any efficacy were natural repellents containing citronella oil. In fact you can pluck citronella fruit straight from the tree and rub it on since it grows wild in Costa Rica. Unfortunately our experience agreed with independent studies that showed citronella oil while approximately as effective as DEET when first applied only lasts a few minutes.
We haven’t had very good luck with gerinol either. Independent studies have shown it to be almost as effective as DEET for at least 30 minutes but it seemed to attract mosquitoes to me.
Oil of lemon eucalyptus (para-menthane-3,8-diol) and IR3535 (3-[N-butyl-N-acetyl]-aminopropionic acid, ethyl ester) are other “biopesticide repellents,” meaning synthetic or extracted chemicals from natural sources that the EPA has approved as mosquito repellents. Neither worked well for me and I had to switch to DEET within a few minutes.
In general we found that the natural repellents did reduce the number of mosquito bites for a short time but we weren’t willing to reapply every few minutes. The effectiveness of natural repellents seems to vary a lot depending on the person using them so you may want to give some of the above a try.
Are Natural Products Safer?
Well, they may sound safer at first, but consider this list.
- phospholipase A2
- (Z)-methyl isoeugenol
Three of the above compounds are some of the fifty-plus components identified so far from citronella oil and one (phospholipase A2) is an active component of cobra venom.
If you knew that, then you may actually have some idea of what you’re rubbing on when you use a natural repellent. The toxicity and potential carcinogenicity of natural repellents is not rigorously tested because they are not highly regulated like synthetic compounds.
Natural repellents may be safer but no one has really checked. DEET and picaridin on the other hand have undergone exhaustive testing by the EPA and others and found to have only a few minor associated risks which are far outweighed by their effectiveness in preventing serious diseases like malaria, west nile and dengue.