The use of combustion to deter biting insects is a long-standing practice that works by two primary mechanisms. The physical presence of smoke interferes with a mosquito’s ability to locate a host by confusing its sensitive receptors. Burning certain materials also releases volatile chemical agents that actively repel or even incapacitate the insects. The heat of the burn disperses these protective compounds into the air.
Manufactured Smoke Repellents and Their Ingredients
Commercial mosquito control often relies on products designed for slow combustion, such as coils, incense sticks, and specialized candles. These products are engineered to smolder for extended periods, steadily releasing active ingredients into the surrounding air. The most potent of these repellents contain compounds derived from or chemically related to the natural insecticide pyrethrum.
Pyrethrum is naturally extracted from the dried flowers of the chrysanthemum plant, Chrysanthemum cinerariifolium, and its active components are known as pyrethrins. When heated, these pyrethrins volatilize and act quickly on the insect’s nervous system, causing a rapid “knockdown” effect. This neurotoxic action leads to paralysis and eventual death for the insect.
Many modern products utilize pyrethroids, which are synthetic analogs of natural pyrethrins, such as allethrin, designed for greater stability and effectiveness outdoors. These compounds maintain the same neurotoxic mechanism against mosquitoes but are less susceptible to degradation from sunlight and heat. The insecticide is mixed with a combustible filler material and a binding agent, forming the familiar spiral shape that ensures a burn time of several hours.
Another common ingredient in manufactured repellents is citronella oil, which is derived from the leaves and stems of certain lemongrass species. The repellent properties of this oil come from its main chemical components, citronellal and geraniol. When a citronella candle or incense stick is burned, the heat causes these volatile compounds to evaporate and disperse.
The strong, citrus-like aroma of citronella works by masking the human-specific odors, like carbon dioxide and lactic acid, that mosquitoes use to track targets. While not an insecticide like pyrethroids, citronella creates an olfactive screen that makes it significantly harder for mosquitoes to find people in the immediate vicinity of the smoke.
Burning Natural Plant Materials
A more traditional approach to mosquito control involves burning unprocessed, dried plant matter to release its innate repellent oils. This method, often referred to as “smudging,” works by slowly burning material rather than igniting it with a full flame, maximizing the release of aromatic smoke. Many common herbs and woods contain volatile organic compounds that mosquitoes find highly unpleasant.
For instance, simply tossing dried sprigs of rosemary or sage onto a campfire or barbecue grill releases aromatic smoke that deters flying insects. These culinary herbs contain oils that, when heated, are dispersed into the air to create a localized barrier. The smoke from pine varieties of wood is also noted for its effectiveness as a general mosquito deterrent.
Other plants like lavender and basil are also known to contain insect-repelling essential oils. The strong scent of dried basil, for example, is effective against both mosquitoes and flies, while the oils in lavender are known to repel a wide range of pests.
Safety Considerations for Smoke-Based Repellents
While effective, all smoke-based repellents require careful consideration regarding both fire and health safety. From a fire safety perspective, any burning product, whether a coil or a candle, must be placed on a stable, non-flammable surface, such as a ceramic or metal holder. These devices should never be left unattended and must be kept away from flammable materials, especially outdoors where wind can carry embers.
Regarding health concerns, the inhalation of dense smoke from any source poses a respiratory risk, particularly for individuals with conditions like asthma or for young children and pets. Studies have shown that the fine particulate matter (PM) released by a single burning mosquito coil can be equivalent to the PM emissions of up to 137 cigarettes.
In addition to particulate matter, the incomplete combustion of materials in mosquito coils can release harmful substances, including formaldehyde. For this reason, manufactured coils and incense sticks are best used outdoors or in very well-ventilated areas. Prolonged exposure to the smoke, especially in enclosed spaces, should be avoided to mitigate the risk of respiratory irritation.