Sept. 16, 2004 -- Products that contain a combination of sunscreen and the insect repellent DEET may save time, but they may also increase certain risks, according to new research.
DEET is the most popular active ingredient in insect repellent, and its use is recommended to reduce the risk of diseases that are spread by insects, such as the West Nile virus.
Researchers say although DEET has a low risk of side effects when used on its own, the effects of using products that combine DEET with other substances that increase its potency deserves further study.
"DEET has an unbelievably superb safety record; it's been used on millions of people and it's critical that people don't get the wrong message," says researcher Edward A. Ross, MD, an associate professor of medicine at the University of Florida Health Science Center, in a news release. "People should continue using DEET because of the very real risks of mosquito and insect-borne illnesses, such as West Nile encephalitis, but use it in the lowest effective concentration, especially when you use it in combination with other topical lotions or in children."
"A lot of people think if a little bit of something is good, a lot is even better," says Ross. "We don't think this is true for DEET. So the message is not to go for the higher percentage, especially when you're using these other compounds. A little bit is better, not the other way around."
Sunscreen and DEET Creates Potent Mix
In the study, reported in the August issue of Drug Metabolism and Disposition, researchers tested the effects of applying a standard 20% DEET solution vs. a 10% DEET solution plus sunscreen on hairless mice.
Although standard 20% DEET took 30 minutes to be penetrate the skin, the DEET plus sunscreen was detectible in the skin in as little at 5 minutes, even though it contained half as much DEET as the standard solution.
The study also showed that once the DEET penetrated the skin, it was absorbed 3.4 times faster in the combination DEET and sunscreen than with the standard 20% DEET solution.
Researchers say the technology to test skin absorption of chemicals like DEET and sunscreens is readily available, but most manufacturers test these common ingredients individually rather than in combination. They say these findings suggest that more attention should be paid to the possible interactions of these chemicals.
The American Academy of Pediatrics recommends that parents select an insect repellent containing the lowest concentration of DEET possible for their children and that DEET should not be applied more than once a day in children. The Academy also advises against using products that combine sunscreens and DEET because sunscreens must be reapplied.