Mosquito coils are a common, low-cost method for repelling and killing mosquitoes, typically found as an incense-like spiral that slowly smolders for several hours. While effective, burning the coil introduces a complex mixture of chemicals and particulate matter into the air, raising significant questions about safety. The primary concern is how the smoke and its chemical components affect indoor air quality and the long-term health of those exposed.
Active Ingredients and Combustion Byproducts
The insect-repelling action comes from active ingredients, most often synthetic pyrethroids (like allethrin or d-allethrin) or natural pyrethrins derived from chrysanthemum flowers. These insecticides comprise a small percentage of the coil weight (around 0.3% to 0.4%) but are volatilized into the air as the coil burns. Pyrethroids are neurotoxins that disrupt the insect’s nervous system, leading to paralysis or death.
The greater health concern stems from the combustion of the inert filler materials, binders, and dyes that make up the bulk of the coil. This smoldering process generates a substantial amount of smoke laden with fine particulate matter (PM), particularly PM2.5. PM2.5 is small enough to penetrate deep into the human lungs. Studies show that burning a single mosquito coil can release the same amount of PM2.5 mass as burning between 75 and 137 cigarettes.
The combustion process also releases a suite of toxic gaseous pollutants beyond the physical smoke particles. These include formaldehyde, polycyclic aromatic hydrocarbons (PAHs), and various volatile organic compounds (VOCs), many of which are known or suspected carcinogens. In some formulations, a synergist like octachlorodipropyl ether (S-2) is used, and its combustion can produce bis(chloromethyl)ether (BCME), a potent lung carcinogen. The high concentration of these pollutants can cause indoor air quality to substantially exceed established health standards.
Health Effects of Inhaling Coil Smoke
Exposure to mosquito coil smoke causes health effects from both particulate matter and active insecticide chemicals. The sheer volume of fine particulate matter (PM2.5) is a major respiratory irritant, causing acute symptoms like coughing, wheezing, and throat discomfort. Daily or prolonged use, especially in poorly ventilated spaces, increases the risk of developing chronic respiratory diseases. Constant exposure can also exacerbate existing conditions such as asthma and Chronic Obstructive Pulmonary Disease (COPD).
The chemical components of the smoke also contribute to negative health outcomes. Formaldehyde, a combustion byproduct, can cause watery eyes, nasal irritation, and respiratory distress. Long-term exposure to carcinogens in the smoke, such as PAHs and BCME, has been associated with an increased risk of lung cancer. Some research suggests that individuals who frequently use coils indoors face a significantly elevated risk of developing lung cancer compared to non-users.
The active pyrethroid insecticides can also produce systemic effects, though they are considered less toxic to mammals than insects. Acute pyrethroid toxicity can manifest as headache, nausea, incoordination, and skin irritation. Vulnerable groups face greater risks, including infants and young children who may not efficiently metabolize the chemicals, and individuals with pre-existing respiratory conditions. Pregnant people are also a sensitive population due to potential adverse effects on the developing fetus.
Guidelines for Minimizing Exposure
For those who choose to use mosquito coils, strict guidelines are necessary to mitigate health risks. The most important step is to use coils exclusively in well-ventilated areas, ideally outdoors, to allow rapid dispersal of smoke and pollutants. Coils should never be burned overnight in bedrooms or other enclosed spaces.
If a coil must be used indoors, ensure windows and doors are open to maximize air exchange, and limit the burning time to the minimum duration needed for mosquito control. Position the burning coil far away from people, especially children, pets, and pregnant individuals, to reduce direct inhalation of the concentrated smoke plume. Maintain a safe distance from food preparation areas, as the smoke can contaminate items. The coil should always be placed on a fireproof surface and fully extinguished before leaving the area unattended.
Safer Mosquito Control Methods
Many alternatives offer effective mosquito control without the risk of smoke inhalation and chemical combustion byproducts. Physical barriers provide a simple, non-chemical defense, such as installing fine-mesh screens on windows and doors. Sleeping under a permethrin-treated mosquito net offers reliable overnight protection, particularly in high-risk areas.
Topical repellents applied directly to the skin are highly effective and offer targeted protection. The most scientifically supported options include products containing DEET (N,N-Diethyl-meta-toluamide) and Picaridin (Icaridin). Oil of Lemon Eucalyptus (OLE), with its active ingredient p-menthane-3,8-diol (PMD), serves as a plant-based alternative that also offers good protection.
Other non-combustion devices are available, such as electric vaporizers that use a heating element to release pyrethroid insecticides from a mat or liquid refill without producing smoke. While these still use insecticide, they eliminate the particulate matter and toxic combustion byproducts associated with coils. Devices using metofluthrin are designed to create a mosquito-free zone without heavy smoke. Electronic ultrasonic devices are not recommended, as scientific studies have shown them to be unreliable for repelling mosquitoes.