The physical and chemical properties of the mosquito coil, a commonly used mosquito repellent in Asia and South America, were analysed. The smoke emitted from the burning mosquito coil consists of submicron particles (diameter less than 1 micron) coated with a considerable amount of heavy metals, allethrin and a wide range of organic vapors, such as phenol and o-cresol. Therefore, a lengthy exposure to this smoke will cause adverse effects on the consumers.