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Insect & Mosquito Repellents

The Backstory

Mosquitoes transmit some of the most devastating diseases on earth: malaria, dengue fever and yellow fever. And while most residents of the U.S. are safe from these illnesses, mosquitoes in this country can carry West Nile virus, a disease that affects the nervous system. Just as dangerous are the illnesses carried by ticks. Rocky Mountain spotted fever is a bacterial infection that kills about 5 percent of the people who contract it. Lyme disease, another bacterial infection transmitted by deer ticks, isn't fatal, but left untreated, it can damage the heart and the nervous system and lead to joint problems. In light of these, and other less severe diseases carried by ticks and mosquitoes, it's important to protect yourself. However, the chemicals we use to ward off insects can cause more harm than good.

Bug Sprays
Most insect repellents sold today contain the synthetic chemical DEET (short for N,N-Diethyl-meta-toluamide). There's been a great deal of controversy surrounding the use of DEET, with major medical organizations such as the Centers for Disease Control and Prevention and the American Academy of Pediatrics claiming that it is safe and effective if used properly. Other academic studies, however, have found that DEET can slow motor skills and impair central nervous system function, especially if used with permethrin, a chemical used on some outdoor clothing to repel insects. Most of the problems with DEET were found in people who used DEET-containing bug sprays regularly (once a day for five days or longer), and those problems ranged from mild skin irritation and headache to seizures, restlessness, rapid loss of consciousness and even death. DEET has also been detected in waterways, and the fact that it doesn't biodegrade suggests that it might wind up in our drinking water.

Chemically Treated Clothing
As mentioned previously, many outdoor clothing manufacturers have started selling clothes treated with permethrin to deter mosquitoes, ticks and other biting insects. A synthetic version of the pyrethrin found in chrysanthemums, permethrin comes out of the clothing as you sweat, and military research has shown that it can be absorbed by the skin. Exposure can cause asthma attacks, headaches and nausea, and the chemical is a suspected endocrine disrupter. Furthermore, permethrin comes out of clothes when they're washed, threatening waterways and lulling you into a false sense of safety; many manufacturers claim the chemical will remain on clothes for 25 washings, but if you don't count those carefully, you might not take the proper precautions when you wear the clothes.

Municipal Sprays
In areas with severe mosquito or tick problems, local pest control agencies or health departments may spray entire neighborhoods and communities to keep bug populations down. Often they'll use a class of chemicals called organophosphates (OPs), two of the most common being malathion and naled. Malathion is considered less toxic than naled but both can cause skin irritation, and like other members of the OP family, can spur neurological problems if there is long-term exposure. These chemicals are also highly toxic to bees, and given recent die-offs of entire honeybee populations, use of these chemicals is particularly troubling.

Another class of anti-mosquito and anti-tick chemicals is pyrethroids, synthetic chemicals similar to the natural mosquito repellant, pyrethrin, produced by chrysanthemums. Insecticides that fall into this category usually end in "-thrin," for instance permethrin, resmethrin and d-phenothrin. Experts have relatively few concerns over the acute toxicity of pyrethroids, but they can trigger skin and respiratory irritation. Over the long term, pyrethroids may interfere with the immune system (which can lead to allergy problems), and there is some evidence that they disrupt human hormone functions.

Finally, one method of mosquito control involves the use of "larvacides," chemicals put in waterway to prevent breeding. Sometimes larvacides are made with bacteria that kill larvae when eaten, and others use chemicals such as methoprene. While not toxic to humans, methoprene does cause deformities in some aquatic species, and it builds up in the fatty tissue of some types of edible fish.