Mosquitoes transmit disease to more than 700 million people every year. Not only is the buzzing of mosquitoes irritating and nerve wrecking, their bite leaves its reminder with several days of localized itching. Some of the diseases transmitted in the United States include several different types of encephalitis (inflammation of the brain) including St. Louis equine, western equine, eastern equine and La Crosse encephalitis. In the fall of 1999, the West Nile Virus, which is transmitted by mosquitoes, was first detected in the United States. In the year 2000, there were more than 2,000 cases of West Nile encephalitis involving 27 states, and the Center for Disease Control anticipates the disease will continue to spread and infect more people.

Over the years, the mosquito has become a very sophisticated "dive bomber" to attack the unaware human. There are three main weapons the mosquito utilizes to prepare for its attack. First, the mosquito has chemical sensors that, from 100 feet away, can detect carbon dioxide which humans exhale. This assures the mosquito that there is a warm-blooded animal in the vicinity. Second, the mosquito has sophisticated "motion detectors" that help identify any movement by humans. Third, heat sensors detect heat and help the mosquitoes find warm-blooded animals.

It is obviously important for you to find the insect repellent that is most effective. Commercially available insect repellents can be divided into two categories-synthetic and plant-based oils. A medical review in the prestigious New England Journal of Medicine clearly chooses as the repellent of choice the chemical N,N-diethyl-3-methylbenzamide, which is now called DEET. Citronella and other plant oils were reported to be of little effectiveness.

DEET is available in different concentrations, varying from 4% to 30% DEET. In tests, the 4% protection lasted 88 minutes while the 23% lasted five hours. The 30% concentration should last even longer. The "slow-release" did not work as well as the alcohol-based DEET preparation.

Be sure to read the label carefully for the proper concentration and "cautions." Infants should not use high concentrations of DEET over large areas of the body.

Enjoy the outside but respect the small flying villain called a mosquito. It just takes one bite to spread disease.

Dr. Robert Overholt has been in private practice for more than 30 years. He is the host of the television program "The Dr. Bob Show" airing weekly in 13 million homes on the Goodlife Television Network. If you have a question for Dr. Bob, write "The Dr. Bob Show" at 6700 Baum Drive, Suite 1, Knoxville, TN 37919 or send your e-mail to letters@drbobshow.com.