CORVALLIS - As West Nile virus surfaces in Oregon, the last remaining continental state to encounter the disease, Oregonians may be tempted to douse themselves in DEET - a potent and popular insect repellent - to protect against disease-carrying mosquitoes.

The product is generally safe if applied properly, but DEET can pose health risks if you fail to follow label instructions, says Dr. Daniel Sudakin, a toxicologist at Oregon State University.

Sudakin is an assistant professor in OSU's Department of Environmental and Molecular Toxicology who has a medical degree from Wayne State University. He has spent the last several years reviewing available epidemiological data on human exposures and subsequent adverse reactions to DEET.

He's found that millions use products containing DEET, recommended by the Centers for Disease Control, safely and effectively each year. However, hundreds of adverse reactions, most commonly affecting the skin, are reported each year. The majority of these adverse reactions occur when DEET is overused or misused, Sudakin emphasized.

"It is very important not to apply over cuts, wounds or irritated skin, which more easily absorbs the chemical," warned Sudakin. "You want DEET on the surface of exposed skin only."

He also cautions that young children should never apply DEET to themselves because they may be unnecessarily overexposed. DEET should never be used underneath clothing as that can enhance absorption across the skin. After returning indoors, users should wash treated skin with soap and water - particularly if using a high concentration product.

"People think more is better when it comes to DEET," Sudakin said.

While DEET is the most effective repellent, he suggests that people use a concentration appropriate for the amount of time spent outdoors. For example, a product with a concentration of less than 10 percent is effective for people that will be outside one to two hours. In fact, concentrations containing 10 percent appear to be as effective as 30 percent. While there are products with 100 percent DEET, they may be useless.

"Beyond 40 to 50 percent, there's just not much more protection," he said.

Not surprisingly, young infants require special care. Recently, the American Academy of Pediatrics recommended that children under two months of age should not be exposed to DEET.

DEET isn't the only insect repellent on the market. Alternative insect repellents registered by the EPA tend to be botanically derived, containing oils such as eucalyptus, soybean or citronella. These products typically do not last as long as DEET and can carry their own risk.

"People tend to consider these as inherently safe," Sudakin said, "but in reality these can cause allergic reactions as well."

With only six weeks left until mosquito season ends, no human cases have yet been reported in Oregon. But horses and crows testing positive in eastern Oregon herald its arrival. While Sudakin doesn't think Oregon's West Nile virus situation is as urgent as in nearby states, he cautions that the virus continues to surprise.

"Nobody thought it would turn up in places like Arizona," he pointed out, adding that West Nile could be cause for greater concern in Oregon next summer.

Citizens with specific questions about DEET should contact the National Pesticide Information Center at (800) 858-7378 or online at www.npic.orst.edu.