From New World Encyclopedia

IUPAC name N,N-Diethyl-3-methylbenzamide
Other names N,N-Diethyl-m-toluamide
CAS number [134-62-3]
Molecular formula C12H17NO
Molar mass 191.27 g/mol
Density 0.998 g/mL
Melting point

-45 °C

Boiling point

288-292 °C

Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

DEET is a chemical, N, N-Diethyl-m-toluamide, that acts as an insect repellent to prevent bites from mosquitoes, fleas, biting flies, and other insects, as well as ticks (arachnids). It is the most common active ingredient in insect repellents, popular in liquid sprays, lotions, and sticks, and is intended to be applied to the skin or to clothing. It is estimated that every year roughly thirty percent of the United States population uses various products that contain DEET (NPIC 2008).

In addition to being a nuisance, the bites of a number of insects and ticks pose health risks. For example, ticks bites may transmit Lyme disease, several rickettsioses, tick-borne meningoencephalitis, and other tick-borne diseases, and mosquito bites may transmit malaria, dengue fever, West Nile virus, and eastern equine encephalitis. Therefore, the use of an insect repellent is an important measure for prevention of these vector-borne diseases. DEET is one of the most effective insect repellents known, and is considered safe for humans and the environment when used properly, although the American Academy of Pediatrics recommends not using on infants less than two months old (CDC 2008).

Overview, description and method of action

Deet is a slightly yellow, almost colorless liquid at room temperature. Its IUPAC name is N,N-Diethyl-3-methylbenzamide and it also is known as N,N-Diethyl-m-toluamide. It can be prepared from m-methylbenzoic acid and diethylamine. This can be achieved by preparing the acid chloride and subsequently reacting that with the diethylamine. It can be distilled under vacuum: boiling point 111°C at 1 mm Hg. DEET has a faint odor and does not easily dissolve in water (NPIC 2008). DEET is an effective solvent (Petherick 2008), and may dissolve (part of) some plastics, rayon, spandex, other synthetic fabrics, leather, and painted or varnished surfaces. The chemical formula of DEET is C12H17NO.

DEET was developed by the United States Army for protection of soldiers in insect-infested areas, following its experience of jungle warfare during World War II. It entered military use in 1946 and civilian use in 1957. Originally tested as a pesticide on farm fields, the United States Government applied it for war time usage, particularly when in Vietnam and around that region of Asia.

The mechanism of how DEET works is not completely understood for all insects (NPIC 2008). In general, DEET is believed to work by blocking insect olfactory receptors for 1-octen-3-ol, a volatile substance that is contained in human sweat and breath. DEET effectively "blinds" the insect's senses so that the biting/feeding instinct is not triggered by humans or animals that produce these chemicals. DEET does not appear to affect the insect's ability to smell carbon dioxide, as had been suspected earlier (Petherick 2008; Ditzen et al. 2008).

Use of DEET as an insect repellent

DEET is available in many insect repellents

DEET is used in a wide variety of products, including liquid sprays, lotions, and sticks. The concentration can vary considerably, such as 4.75 percent, 20 percent, 23.8 percent, up to 100 percent. Various studies have found a direct correlation between DEET concentration and hours of protection against insect bites. Fradin and Day (2002) found that a product with 23.8 percent DEET provided an average of five hours of protection against insect bites, compared to four hours of protection offered by a product with 20 percent DEET, while a 6.65 percent DEET product provided almost two hours of protection, and a product with 4.75 percent DEET provided roughly 1.5 hours of protection. Matsuda et al. (1996) found a 100 percent DEET solution offered up to 12 hours of protection, while several lower concentration DEET formulations (20-34 percent) offered three to six hours of protection. Other research has corroborated the effectiveness of DEET (Williamson 2002).

Effects on health

One can be exposed to DEET through contact with the skin or eyes, inhalation, or swallowing. For example, one may inhale the spray if used in indoor spaces where vapors remain and may swallow DEET if the hands are not washed after applying (NPIC 2008). If DEET gets into the eyes, one can experience pain, irritation, and watery eyes, and extended exposure to the skin can result in redness, a rash, irritation, and swelling (NPIC 2008). Swallowing DEET can result in upset stomach, vomiting, and nausea (NPIC 2008).

As a precaution, manufacturers advise that DEET products should not be used under clothing or on damaged skin, and that preparations be washed off after they are no longer needed or between applications (CDC 2008).

In the DEET Reregistration Eligibility Decision (RED), the EPA reported 14 to 46 cases of potential DEET-associated seizures, including 4 deaths. The EPA states: "…It does appear that some cases are likely related to DEET toxicity," but observed that with thirty percent of the U.S. population using DEET, the likely seizure rate is only about one per 100 million users (EPA 1998). There has been a report that "Everglades National Park employees having extensive DEET exposure were more likely to have insomnia, mood disturbances, and impaired cognitive function than were lesser exposed co-workers" (EXTOXNET 1997).

The American Academy of Pediatrics (AAP) states that a concentration of 10 percent appears to be as safe for children as products with a 30 percent concentration, although they do not recommend use of repellents with DEET for infants less than two months old (CDC 2008). They further recommend that DEET be applied no more than one time a day for children older than two months and that the lowest concentrations of DEET available be used (NPIC 2008). It is generally not advised to apply on the hands of children, nor near the mouth or eyes. Note that these are recommendations for children not considered to be at risk of serious vector-borne diseases.

Studies have shown that a small amount of the DEET applied to skin is taken into the body, and that this intake is greater if DEET and alcohol both are applied to the skin. The DEET taken into the body remains in the blood for up to 12 hours. However, all of the DEET is broken down by the liver into smaller chemicals and eliminated from the body, largely through the urine, with nearly all of the DEET eliminated from the body within 24 hours of application (NPIC 2008).

Evidence has not been found that DEET causes cancer in humans or animals, and it has been classified by the U.S. Environmental Protection Agency as "Not Classifiable as a Human Carcinogen," meaning there is not enough evidence that it does or does not cause cancer (NPIC 2008).

Effects on the environment

Although few studies have been conducted to assess possible effects on the environment, DEET is a moderate chemical pesticide and may not be suitable for use in and around water sources. Because it is so commonly used, it has been found in wastewater and other bodies of water impacted by wastewater. DEET has been detected in significant levels in waterbodies as a result of production and use, such as in the Mississippi River and its tributaries, where a 1991 study detected levels varying from 5 to 201 ng/L (Zeiger et al. 1999).

In the soil, it can be broken down by fungi, bacteria, and other microorganisms, and experiments have shown that fungal and bacterial breakdown products were less toxic than DEET itself (NPIC 2008). Likewise, as a mist or vapor in the air, it breaks down as well (NPIC 2008).

DEET has been found to have a slight toxicity for coldwater fish such as the rainbow trout (EPA 1980) and the tilapia (Mathai et al. 1989), and it has also been shown to be toxic for some species of freshwater zooplankton (Seo et al. 2005). In very high concentration, about 75,000 times greater than the highest concentrations found in streams or wastewater, DEET was extremely toxic to freshwater fish and insects, killing half of the fish and insects (NPIC 2008). DEET is not expected to bioaccumulate.


Picaridin (KBR 3023) is another repellent recommended by the Centers for Disease Control and Prevention (CDC); permethrin is recommended for use on clothing, shoes, bed nets, and camping gear, but not directly to the skin (CDC 2008).

Studies have shown eucalyptus-based repellents that contain the natural oil eucalyptol to be a highly effective and nontoxic alternative to DEET (O'Conner 2008). Oil of lemon eucalyptus was found to offer similar protection as repellents with low concentrations of DEET (CDC 2008).

Citronella oil has been used as an insect repellent for 60 years (EPA 1999). Its mosquito repellent qualities have been verified by research (Jeong-Kyu 2005; Jantan and Zaki 1998; Trongtokit et al. 2005); however, the repellency duration of DEET is much greater (Fradin and Day 2002).

A test of various marketed insect repellents by an independent consumer organization found that synthetic repellents (DEET and picaridin) were more effective than repellents with "natural" active ingredients. All the synthetics gave almost 100 percent repellency for the first 2 hours, whereas the natural repellent products tested were most effective for the first 30-60 minutes and then required reapplication to be effective over several hours (Choice 2005). Likewise, the CDC suggests the repellents with DEET or picaridin provide longer-lasting protection than other products, while oil of lemon eucalyptus provides longer-lasting protection than other plant-based repellents (CDC 2008). While most essential oil based repellents are not as effective as DEET (Fradin and Day 2002; Collins et al. 1993), some research also suggests that some essential oil based formulas are comparable to DEET, and somewhat better specifically as mosquito repellant (Trongtokit et al. 2004).

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