Burning mosquito coils is one of the most popular ways to reduce mosquito bites in many tropical and subtropical countries, especially Asia. Despite their effectiveness, mosquito coils should be used with caution and according to label instructions.
Mosquito coils burn for about 8hr without flame and kill or repel mosquitoes. Although they are recommended for outdoor use, or for use in semi-enclosed patios and porches, coils are often used overnight in sleeping quarters, where elevated exposure may occur as parents seek to protect their children from mosquitoes. While burning, mosquito coils emit chemically complex smoke containing small particles, metal fumes, and vapors.
Coils usually consist of an insecticide or repellent, organic fillers capable of burning with smoldering (sawdust, coconut husks and shells), binder, and additives such as synergists, dyes, and fungicides. The most common active ingredients in coils are various pyrethroids, such as allethrin, d-allethrin, pynamin forte, ETOC. Octachlorodipropylether (S-2) is sometimes used as a synergist or active ingredient and use of such coils exposes humans to some level of bis(chloromethyl)ether (BCME) which is an extremely potent lung carcinogen. Although the U.S. Environmental Protection Agency (U.S. EPA) does not register S-2 for any use, some imported mosquito coils contain this chemical, but their use is illegal in the United States.
Other compounds, released during the burning of mosquito coils (aldehydes, formaldehydes, fine and ultrafine particles, benzene, benzo[a]pyrene, benzo[b]fluoranthene, benzo[k]fluoranthene) are also classified by the U.S. EPA as probable human carcinogens.
Coils are known to aggravate asthma, complaints of acute toxic effects, eye and nose irritation, headache, bronchial irritation, skin reactions are also commonly heard from consumers using these devices. Furthermore, some trials showed that one coil burning for 8 hours releases as much particulate matter as 75 to 137 cigarettes.
All above-mentioned risks are low if mosquito coils are used properly – that is outdoors.