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N,N-diethyl-3-methylbenzamide (en-en-dye-ETH-el-three-METH-el-ben-ZA-mid) is the most commonly used insect repellant in the world. It is probably better known by its common name of DEET. DEET is applied to the skin and clothing to ward off biting insects such as mosquitoes, ticks, chiggers, and fleas. Although it does not kill insects, DEET repels them for several hours after being applied.

N,N-diethyl-3-methylbenzamide is a colorless amber liquid with a faint odor. The compound can exist in any one of three isomers in which the two groups attached to the benzene ring are next to each other (ortho), separated by one carbon (meta), or opposite each other in the ring (para). Although all three isomers are effective as insect repellants, the meta isomer is more effective than the ortho and para isomers and constitutes about 95 percent of the commercial product.



N,N-diethyl-mtoluamide; DEET




Carbon, hydrogen, nitrogen, oxygen






191.27 g/mol


−45°C (−49°F)


160°C (320°F) at 19 mm Hg pressure


Insoluble in water; soluble in alcohol, ether, benzene, and most other organic solvents

DEET was discovered by researchers at the U.S. Department of Agriculture and patented by the U.S. Army in 1946 for use on military personnel working in insect-infested areas. It was not made available to the general public until 1957. Experts now regard DEET as the "gold standard" of insect repellants. It is available in a variety of formulations, including solutions, lotions, creams, gels, aerosol and pump sprays, and impregnated towelettes under names such as Hour Guard 8 and Hour Guard 12, DEET Plus, Sawyers Gold, Off (in many varieties), Ben's Backyard and Ben's Wilderness, Cutter (in many varieties), and Repel (in many varieties).


DEET is made commercially by treating m-toluic acid (C6H4CH3COOH) with thionyl chloride (SOCl2). The product of this reaction, m-toluoyl chloride (C6H4CH3COOCl) is then treated with diethylamine (C2H5)2NH) to obtain N,N-diethyl-3-methylbenzamide.


The mechanism by which DEET repels insects is not completely understood. Current theories suggest that the compound blocks receptors on a mosquito's antennae that help it to locate carbon dioxide and lactic acid, given off in skin perspiration and the breath. Lacking these chemical clues, insects are unable to locate their prey (humans and other animals).

By warding off biting insects, DEET protects against the diseases they carry. Mosquitoes, for example, carry diseases such as malaria, one of the most serious diseases in the world, responsible for an estimated three millions deaths a year; encephalitis, an infection that causes inflammation and swelling of the brain; and West Nile virus, an organism that affects the central nervous system and poses a serious threat to both humans and other animals. Ticks carry Lyme disease, an infection spread by the deer tick that causes a skin rash, joint pain, and flu-like symptoms that can develop into a debilitating and permanent health problem if not treated early.

Interesting Facts

  • The U.S. Environmental Protection Agency (EPA) has estimated that more than two hundred million people around the world use products containing N,N-diethyl-3-methylbenzamide.

DEET is a very safe product when used as directed. It is absorbed rapidly through the skin, with up to 56 percent of the compound penetrating the skin in a six-hour period. Within twelve hours of application, DEET is metabolized by the liver and excreted in the urine. If inhaled or swallowed, however, DEET poses serious health hazards. It may cause headaches, seizures, and swelling of the brain, although these symptoms are very rare among users of the product. Products containing DEET are not recommended on babies under the age of two months, and are now required by the EPA to carry a warning to avoid spraying the product directly into the eyes or open wounds.

Words to Know

One of two or more forms of a chemical compound with the same molecular formula, but different structural formulas and different chemical and physical properties.


"Basic Facts About DEET and DEET-Based Insect Repellents." Consumer Specialty Products Association. http://www.deet.com/deet_fact_sheet.htm (accessed on October 7, 2005).

"DEET." http://www.chem.ox.ac.uk/mom/InsectRepellents/DEET.htm (accessed on October 7, 2005).

Fradin, Mark S., M.D. "Mosquitoes and Mosquito Repellants." Annals of Internal Medicine. June 1, 1998: 931-940. Also available online at http://www.annals.org/cgi/content/full/128/11/931 (accessed on October 7, 2005).

Qiu H., H. W. Jun, and J. W. McCall. "Pharmacokinetics, formulation, and safety of insect repellent N,N-diethyl-3-methylbenzamide (DEET): a review." Journal of the American Mosquito Control Association. March 1998: 12-27. Also available online at http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=98261685&dopt=Citation (accessed on October 7, 2005).

"Review of the Toxicology Literature for the Topical Insect Repellent Diethyl-m-toluamide (DEET)." Department of Health Toxicology Unit (United Kingdom). http://www.advisorybodies.doh.gov.uk/pdfs/reviewofdeet.pdf (accessed on October 7, 2005).

See AlsoCarbon Dioxide; Lactic Acid