Insect repellent

Insect repellent

One of the most widely used ingredients in bug sprays for personal use is N,N-Diethyl-m-toluamide, or DEET, as it's commonly known. DEET is designed to repel, rather than kill, insects. DEET is used by an estimated one-third of the US population each year.

Although DEET is approved by the US Environmental Protection Agency (EPA), it is a known eye irritant and can cause rashes, soreness, or blistering when applied to the skin. Additionally, DEET has been linked to neurological problems; according to the EPA, at least 18 different cases of children suffering adverse nuerological effects, as well as the deaths of two adults, have been associated with DEET. Researchers at Duke University Medical Center have found that DEET causes diffuse brain cell death and behavioral changes in rats.[1]

DEET has been shown to have a negative impact on wildlife and water sources in production and during use. DEET is toxic to birds and aquatic life. DEET has been found in approximately 75 percent of U.S. water sources, including the Mississippi River.[2] Because of this, DEET-containing products should be disposed of properly, such that it will not contaminate soil or water where it can affect wildlife. Also, DEET-containing products should never be worn while swimming or during other activities where a person will be entering water systems.

Chemically treated insect-repellent clothing

Chemically treated insect-repellent clothing may be treated with the pyrethroid pesticide permethrin, a synthetic version of the naturally occurring pesticide pyrethrin found in chrysanthemums. (Permethrin is a contact insecticide that is not intended to be sprayed directly on skin.) Over 2 million pounds of permethrin are used in the US annually in more than 100 million separate applications, including use in personal bug sprays, and agricultural and residential insecticides.[3]

Permethrin is highly toxic to aquatic organisms and honeybees—concentrations of less than one part per billion can be lethal to some species.[3] Permethrin is so toxic to some aquatic organisms that any detectable level of the chemical in estuarine waters (even less than one part per billion) will likely be associated with negative effects on wildlife, and it can kill some organisms at levels that are not even detectable in water.[4] Although permethrin has a relatively short half-life in the environment, it has routinely been found in ground and surface water at levels that are toxic to wildlife.

Permethrin may cause nervous system complications in humans, ranging from headaches to convulsions and loss of consciousness, as well as asthma attacks, headache, and nausea. Animal studies have indicated reduced fertility and possible immune system damage to fetuses exposed to permethrin, but this has not been observed in humans. The EPA has also classified permethrin as a likely carcinogen.[3]

Background information

Insect repellents or bug sprays discourage insects from landing on, or otherwise touching, the surface to which they are applied, such as skin or clothing, or they kills insects upon contact with the treated surface. Bug sprays can be made from natural or synthetic substances, and vary greatly in their effectiveness, method and duration of action, and toxicity. Some insect repellents are meant to be applied directly to the skin, while others should only be applied to clothing. Insect repellents help prevent the spread of diseases that are carried by insects, such as malaria, West Nile virus, and Lyme disease. DEET acts by masking the chemical signature produced by humans that attracts insects like mosquitoes. Natural alternatives include products made from plant oils like citronella and eucalyptus.


Although DEET has been used by millions of people around the world for over a half-century, there is considerable controversy over its toxicity to humans. Since DEET can easily be absorbed by the skin, there are questions about safe usage over long periods of time, especially at higher concentrations, by pregnant women, and by children.


  • contact insecticide: A substance that is toxic to insects when they come into contact with it.

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