Insect repellents containing DEET dramatically out-performed repellants relying on synthetic derivations and natural oils, according to a recent study in the New England Journal of Medicine.
Dermatologist Mark Fradin told SNEWS® the reason he did the study, which had a timely publication of July 4, was that he'd been asked as a doctor thousands of times which repellant was better or safer, and he could find no consistent data or methodology to provide clear answers.
"It amazed me how much the data varied for each repellent," said Fradin, of Chapel Hill, N.C., who did the study with researcher John Day, Ph.D. of the University of Florida. "Citronella was showing results that varied from 20 minutes to 6 hours."
What Fradin discovered is that there were no standards for testing. In fact, in a number of cases, he found the mosquitoes being used for testing were a variety that did not bite during the day, and yet the test was conducted during the day so it came as no surprise the repellent worked superbly.
"The EPA is looking at establishing standards for testing," Fradin told us. "Having one standard all repellents must adhere to would be nice. Currently, you can use high-density or low-density testing, any species of mosquito. … It doesn't make sense."
So Fradin and his research partner, Day, enlisted the help of 15 test subjects -- five men, 10 women -- willing to stick their arms into controlled cages full of voracious mosquitoes -- the kind that like to bite, of course. Fradin also elected to use a low-density test since that more accurately reflects the outdoor environment. Only mosquitoes that had not been exposed to repellent were used for each test. A total of 720 tests were run with each repellent tested three times on each subject. Elapsed time to first bite was recorded in each case.
The study results revealed the following, in order of effectiveness:
- OFF! Deep Woods with 23.8 percent DEET -- 200 to 360 minutes of protection
- Sawyer Controlled Release with 20% DEET -- 180 to 325 minutes of protection
- OFF! Skintastic with 6.65% DEET -- 90 to 170 minutes of protection
- Bite Blocker for Kids with soybean oil -- 16 to 195 minutes of protection
- OFF! Skintastic for Kids with 4.75% DEET -- 45 to 120 minutes of protection
- Natrapel with Citronella -- 7 to 60 minutes of protection
- Herbal Armor with numerous oils -- 1 to 55 minutes of protection
- Green Ban with Citronella and Peppermint oils -- 1 to 45 minutes of protection
- Buzz Away with Citronella -- 5 to 30 minutes of protection
- Skin-So-Soft Bug Guard with Citronella -- 1 to 30 minutes of protection
- Skin-So-Soft Bath Oil -- 1 to 30 minutes of protection
- Skin-So-Soft Moisturizing Suncare with Citronella -- 1 to 15 minutes of protection
- Gone Original Wristband with 9.5% DEET -- 0.17 to 1.33 minutes of protection
- Repello Wristband with 9.5% DEET -- 0.17 to 0.63 seconds of protection
- Gone Plus Repelling Wristband with Citronella -- 0.17 to 0.48 seconds of protection
What surprised Fradin the most following the study is how wide the spread is from effective to non-effective repellents.
"I honestly thought going into the study that there would be more of a balanced spread. I certainly expected DEET to have long lasting benefits, but what surprised me is that so little else came even close," Fradin said.
Of course, Fradin pointed out that even the numbers realized in his study (www.nejm.org) are not absolutes. The manner in which repellents work is not at all like a sunscreen where you can place a number on it and expect "X" times protection.
We asked Fradin why he did not test products that combine sunscreen and repellent and he told us that he decided against testing them for two reasons. Most important, he says, is that the EPA wants them off the marketplace. The other reason is that he doesn't believe in the concept either.
"Insect repellents should only be applied as needed," Fradin says. "Sunscreen should be applied liberally, frequently, and well before risk. Combine them both and you either put on far too much insect repellent or far too little sunscreen. Either is just as bad."
Fradin also debunked the DEET risk myths.
"DEET has been subjected to more scientific and toxicological scrutiny than any other repellent substance," said Fradin. "It's safety profile over 40 years of use and over 8 billion human applications is remarkable. Like anything else, you have to apply it with common sense -- use only as needed."
Of course, Fradin acknowledged that there are still folks who will want to decide between natural alternatives and DEET.
"If you are going to be traveling to an area where there is a high degree of risk of disease from mosquito bites, DEET is the best alternative to protection and there really is no other choice," he said. "However, if you are simply trying to protect yourself or your kids from nuisance bites, then you can make your choices accordingly."