Pyrethroids are the core ingredients used in making mosquito coils. Produced by plants, these organic compounds have strong insect repellent properties while remaining largely safe for humans.
Some examples of active pyrethroids used in making mosquito coil include pynamin forte, allethrin, d-allethtrin and ETOC. In addition to pyrethroids, mosquito coils may also contain a pesticide such as DEET. Approved by the EPA, DEET is one of the most commonly used ingredients in insect repellent products, including mosquito coils. A common misconception that many people have is that DEET kills bugs. It does not. Instead, it makes it harder for bugs to smell humans, reducing the risk of bites.
Some mosquito coils may also be made with octacholorodipropyl, or S2. Even though S2 is common in other continents, the use of octacholorodipropyl as an active ingredient is banned within the United States by the Environmental Protection Agency because it exposes users to bi-chloromethyl ether, a known lung carcinogen. In addition to chemical compounds, mosquito coils may also include essential oils such as thyme, soybean oil, clove oil, picaridin, citronela and citrus extract. These are designed to improve the smell of the coil. While mosquito coils are not harmful in the short term, studies show that sustained use of mosquito coils can lead to breathing issues such as wheezing and asthma.