Precautions for an Itchy Summer : Abundant water could lead to mosquito outbreak. New repellents promise longer relief.

This year might be itchier than usual for travelers throughout regions of the United States, according to entomologist Chester Moore, who works for the federal Centers for Disease Control in Ft. Collins, Colo. Blame it on the moisture left in the wake of the West’s heavy winter rains and the East’s heavy snows, which can provide ideal breeding grounds, especially for mosquitoes and ticks.

Going abroad for pleasure or business travel won’t solve the problem either, said Moore. “Anywhere you go in the world there is at least one insect that’s a problem,” he said, “except maybe at the North and South poles.”

Avoiding or minimizing insect bites isn’t just a matter of comfort, of course. Mosquitoes can transmit malaria and yellow fever; ticks can transmit Lyme disease. Still other diseases are spread from the bites of fleas and other insects. “Sand flies in the Middle East, South America and Africa transmit leishmaniasis, a parasitic disease that causes skin ulcers,” said Joe Piesman, another CDC entomologist. Dengue fever, spread by mosquitoes, has been rampant in Puerto Rico, he said.

But travelers now have more options in the war on bugs, as manufacturers and entomologists have put their heads together to improve insect repellents.

Most repellents for human use on the market today contain DEET (N, N diethyl-m-toluamide), a chemical developed in the 1950s, said Joe Tavano of the U.S. Environmental Protection Agency, which registers the repellents, approving them as safe when used as directed. Other repellents use citronella--a derivative of the lemon grass plant and the main ingredient in patio candles designed to repel insects--or other substances.

DEET is generally considered the most effective repellent against all insects. But some people suffer side effects such as skin reactions, usually rashes, Tavano said. The higher the concentration of DEET, the longer the protection lasts. At 100% concentration, a DEET repellent will last up to 12 hours, Tavano said; at lower concentrations, about five hours. DEET is thought to work, as it evaporates, by masking the carbon dioxide vapor and hormones given off by human skin--the scent that experts believe attracts bugs. The CDC’s Moore advises sticking with DEET concentrations of 30% or less. DEET-based repellents on the market range from about 6% DEET up to 100%, although many are in the 20%-30% range, Tavano said.

To decrease risk, many manufacturers have embarked on a hunt for low-concentration repellents that last. One result is the controlled-release formulas, introduced in the last two years. Ultrathon Spray Insect Repellent, for instance, has 24% DEET but lasts up to eight hours, said Mike Kies of 3M, the manufacturer. Ultrathon Cream has 33% DEET and lasts up to 12 hours, according to the manufacturer. Both contain a polymer material that controls the evaporation rate of DEET, Kies said.

Some manufacturers are taking another tack, adding ingredients to increase the ways in which the repellent works. One example is DEET Plus, introduced about a year and a half ago by Sawyer Products. The formula includes 17% DEET plus a fly repellent, said Kurt Avery, Sawyer’s president.

Most experts concur that DEET should not be used at all on children under age 2, and that everyone else should be cautious. “Limit your exposure,” said Tom Bartley, an entomologist for the National Pesticide Telecommunications Network. (An EPA program, the network operates a toll-free hot line, 800-858-7378, Monday-Friday, 6 a.m.-4 p.m. PDT, to answer consumer questions.) “You don’t want to inhale or ingest” repellents, Bartley adds. He tells consumers that putting repellent on clothing is better than putting it on skin, and to try to limit skin use to the hands.

“The best idea is still to use protective clothing,” said Dr. Caroline MacLeod, a Miami physician who specializes in tropical and travel medicine. “Wear long pants and long-sleeved shirts.” Use DEET repellent sparingly on exposed skin, she advised. “Put sunscreen on first and DEET on top,” she said. “Don’t get DEET around the eyes or mouth.” If you’re planning to use DEET repellents on a trip, test them out at home first, MacLeod advised, in case of side effects.