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N,N-Diethyl-meta-toluamide, abbreviated DEET, is the most common active ingredient in insect repellents. It is intended to be applied to the skin or to clothing, and is primarily used to protect against arthropod bites. In particular, DEET protects against tick bites (which transmit Lyme disease, several rickettsioses, tick-borne meningoencephalitis and other tick-borne diseases) and mosquito bites (which transmit dengue fever, West Nile virus, Eastern Equine Encephalitis, and malaria).
[edit] HistoryDEET was developed by the United States Army, 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 US Government applied it for war time usage, particularly in Vietnam and Southeast Asia. [edit] Mechanism of actionDEET was historically believed to work by blocking insect olfactory receptors for 1-octen-3-ol, a volatile substance that is contained in human sweat and breath. The prevailing theory was that DEET effectively "blinds" the insect's senses so that the biting/feeding instinct is not triggered by humans or animals which produce these chemicals. DEET does not appear to affect the insect's ability to smell carbon dioxide, as had been suspected earlier.[1][2] However, more recent evidence shows that DEET serves as a true repellent that acts because it is unpleasant to the insect. A type of olfactory receptor neurons in special antennal sensilla of mosquitoes has been identified that is activated by DEET as well as other known insect repellants such as eucalyptol, linalool, and thujone. Moreover, in a behavioral test DEET had a strong repellant activity in the absence of body odor attractants such as 1-octen-3-ol, lactic acid, or carbon dioxide. Female and male mosquitoes showed the same response.[3][4] [edit] ChemistryA slightly yellow liquid at room temperature, 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.[citation needed] [edit] Concentrations
DEET is often sold and used in concentrations up to 100%. Consumer Reports found a direct correlation between DEET concentration and hours of protection against insect bites. 100% DEET was found to offer up to 12 hours of protection while several lower concentration DEET formulations (20%-34%) offered 3-6 hours of protection.[5] Other research has corroborated the effectiveness of DEET.[6] The Center for Disease Control recommends 30-50% DEET to prevent the spread of pathogens carried by insects.[citation needed] [edit] Effects on healthAs 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.[7] DEET can act as an irritant;[1] in rare cases, it may cause skin reactions.[7] In the DEET Reregistration Eligibility Decision (RED), the United States Environmental Protection Agency (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 30% of the US population using DEET, the likely seizure rate is only about one per 100 million users.[8] The Pesticide Information Project of Cooperative Extension Offices of Cornell University states 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". [9] The American Academy of Pediatrics found no difference in safety for children, between products containing 10% and 30% DEET, when used as directed, but recommends that DEET not be used on infants less than two months old.[7] [edit] Effects on materialsDEET is an effective solvent,[1] and may dissolve (part of) some plastics, rayon, spandex, other synthetic fabrics, leather, and painted or varnished surfaces including nailpolish. [edit] Effects on the environmentAlthough 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.[citation needed] Though DEET is not expected to bioaccumulate, it has been found to have a slight toxicity for coldwater fish such as the rainbow trout[10] and the tilapia,[11] and it has also been shown to be toxic for some species of freshwater zooplankton.[12] 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. [13] [edit] AlternativesStudies have shown eucalyptus-based repellents which contain the natural oil eucalyptol to be a highly effective and nontoxic alternative to DEET.[14] Also, plants such as lemon grass have proven effective against mosquitos. Icaridin is another insect repellent of strength comparable to DEET, but it is less irritating and doesn't dissolve plastics.[15] A test of various marketed insect repellents by an independent consumer organization found that synthetic repellents, including DEET, were more effective than repellents with ‘natural’ active ingredients. All the synthetics gave almost 100% 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.[16] Citronella oil has been used as an insect repellent for 60 years.[17] Its mosquito repellency qualities have been verified by research,[18] [19][20] however, the repellency duration of DEET is much greater.[21] While most essential oil based repellents are not as effective as DEET,[21][22] research also shows that some essential oil based formulas can be comparable to DEET, and somewhat better specifically as mosquito repellant. [23] Research suggests that distilled nepetalactone, the active ingredient in catnip, repels mosquitoes ten times more effectively than DEET,[24] but that it is not as effective a repellent on skin.[25] [edit] See also[edit] References
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