sealPurdue News

July 10, 1998

Beat the bite: Mosquito repellents that work

WEST LAFAYETTE, Ind. -- For many people, citronella candles are a summertime essential to keep mosquitoes at bay.

But Ralph Williams, a Purdue University entomologist, said citronella candles, mosquito coils and other airborne repellents have limited effectiveness because shifting winds can blow the repellents away from the intended area.

The best bets for mosquito protection, he said, are repellents registered with the Environmental Protection Agency as pesticides. Registration ensures a regulated level of safety, testing and effectiveness. Consumers should check for an EPA registration number on the label of insect repellents.

Williams said he uses spray-on repellent, which can provide protection for up to five hours, depending on the amount of perspiration, skin rubbing, temperature and the abundance of mosquitoes.

He said Deet is one of the most effective insect repellent ingredients on the market. Based on extensive toxicity testing, the EPA recently concluded that the normal use of Deet does not present a health concern to the general population. There had been reports that Deet could cause skin and central nervous system problems when applied directly to the skin. Purdue's entomology department encourages closely following label instructions on repellents that contain Deet. The experts recommend using Deet because of its high effectiveness, but using products that contain smaller concentrations of Deet -- 20 percent to 30 percent -- and applying the repellent to clothing rather than directly to skin.

And what about new types of repellents such as bracelets? Williams issues a word of caution.

"It's not that these repellents are dangerous," he said. "They just tend not to be very effective. Mosquitoes are smart and will find unprotected areas."

The bracelets work as a physical deterrent by making the atmosphere around them unpleasant to mosquitoes. Body parts farther away from the bracelet have lower concentrations of repellent around them. Williams said mosquitoes will target those less concentrated areas.

Williams also said granular yard applications, such as Mosquito Beater, can be effective in repelling mosquitoes for six to eight hours. He cautioned that electronic devices advertised as physical attractants are limited in use and should be thoroughly investigated before being purchased. Recent field tests have shown that electrocuting devices using ultraviolet light as an attractant are ineffective in reducing mosquito populations and biting activity.

To help prevent mosquito bites, Williams said it is helpful to wear light-colored clothing, which holds less heat. Wearing dark clothes can result in more heat buildup, therefore increasing body odor-- which acts as a mosquito attractant.

If you are bitten by a mosquito, the best treatment is an antihistamine, Williams said. When a mosquito bites, she (only female mosquitoes bite) injects a salivary solution into the body. The body releases histamines to combat this foreign material.

These histamines result in the itching and swelling associated with mosquito bites. Overzealous scratching can break the skin and result in secondary infections. Williams suggested applying a topical antihistamine to relieve the itching and swelling.

Mosquitoes feast not only on human blood, but also on the blood of other mammals. Generally animals are not harmed by mosquitoes, but some mosquito species may play a role in transmitting heartworm to dogs. During severe mosquito infestations, keep pets inside and avoid walking them during prime mosquito feeding time. Williams also suggested talking with a veterinarian about preventative measures for dog heartworm.

Mosquitoes have been seen in force this year as a result of excessive rains. There are more than 50 known species of mosquitoes in Indiana. They breed in standing water and have a life cycle of seven to 10 days. Elimination of potential breeding grounds is one way to help combat mosquito outbreaks, Williams said. This includes draining water from potential breeding sites such as roof gutters, old tires, bird baths and flower pots.

Source: Ralph Williams, (765) 494-4560; e-mail,

Writer: Jane Houin, (765) 494-8402; e-mail,

Purdue News Service: (765) 494-2096; e-mail,

* To the Purdue News and Photos Page