Mosquito coils equivalent to smoking 60 cigarettes — and bad for the planet, too

A mosquito coil burns indoors. [Provided by reader]

"I've been using them every time I want to keep mosquitoes away … "

With cool breezes and mild sunshine, the weather these days is perfect for outdoor activities — camping, strolling, hiking.

But there is an unwelcome guest: mosquitoes, which tend to multiply around this time of year. One of the most common remedies is the mosquito coil, a slow-burning spiral that releases insect-repelling smoke.

It turns out, however, that the smoke from these coils may be harming not only human health but also the environment.

A swarm of mosquitoes clings to a window screen. [Herald DB]

Research has found that the ultrafine particles produced by burning a mosquito coil can rival those from smoking dozens of cigarettes. Carbon emissions from coils have also been found to exceed those of other mosquito-repellent types.

Recent domestic studies have raised further concerns about the release of harmful substances and the health risks of prolonged exposure — suggesting that the effort to avoid mosquitoes may end up hurting both people and the planet.

A carbon-emissions comparison of three types of mosquito repellent — spray, electric liquid vaporizer and combustion coil — commissioned from climate-tech firm Ohu Dusi Lab found that burning a mosquito coil for one hour produces 67.8 grams of carbon emissions.

By contrast, the spray type emits just 1.16 grams — about 58 times less than the coil. The electric liquid vaporizer produces 3.78 grams, roughly one-eighteenth of the coil's output.

The difference comes down to how each product works. A combustion coil is made by combining insect-repelling compounds with wood powder, known as "mokbun." When lit, the wood powder smolders slowly, releasing the active ingredients into the air.

In other words, combustion is continuous for as long as the coil is in use, and carbon is released into the air throughout that process. The electric liquid vaporizer, by contrast, uses heat to volatilize the active compound. Electricity generation does produce carbon, but the product itself is never burned directly.

When total lifecycle emissions — covering production, use and disposal — are measured for a single product, the electric liquid vaporizer comes out highest at 1,700 grams, followed by the combustion coil at 406 grams and the spray at 291 grams. That does not, however, mean the electric vaporizer is worse for the environment overall.

The electric vaporizer's body can be reused repeatedly, with only the liquid cartridge replaced. Spray products can also be used up to about 250 times per unit. A combustion coil, on the other hand, is gone after a single use. That is why the environmental burden of coils grows significantly when compared on an equal-use-time basis.

Carbon is not the only concern. Mosquito coils have also been found to pose direct risks to human health, because the smoke they produce can be inhaled directly.

Analysis suggests the level of harmful substances generated can even exceed that of cigarette smoke. A 2007 study by a research team led by Yang Won-ho, a professor in the Department of Industrial Health at Daegu Catholic University, compared pollutants from burning a mosquito coil in a poorly ventilated test space with those from cigarette smoke. The findings were published in the Journal of the Korean Society for Indoor Environment.

The study found that the mass of ultrafine particles produced by burning a single mosquito coil was equivalent to smoking 20 to 58 cigarettes. Formaldehyde emissions from one coil were comparable to burning up to 27 cigarettes.

"These results were obtained under worst-case conditions in an enclosed space smaller than a typical room, but mosquito coils may release more harmful air pollutants than cigarette smoke," the researchers said. "People should use alternative repellents or ensure ventilation at the same time."

Research into the health hazards of mosquito coils has continued in recent years. A Korea University research team published findings in the international journal Journal of Hazardous Materials in July, analyzing household insecticides commonly used in South Korea.

The products examined were everyday items: five aerosol sprays, five liquid electric mosquito repellents, five mat-type electric repellents and four combustion mosquito coils.

The results showed that combustion coils continuously release a range of harmful substances into the air while burning — including benzene and toluene — unlike the other product types, which do not involve direct combustion.

Benzene is of particular concern. The International Agency for Research on Cancer classifies it as a Group 1 carcinogen, meaning it has been confirmed to cause cancer in humans.

The researchers also calculated the potential health effects of prolonged inhalation of these substances.

For health impacts other than cancer, none of the products tested exceeded the threshold for concern. Combustion coils were the exception. The analysis found that repeatedly inhaling the smoke indoors without ventilation over a long period could push the cancer risk from benzene above the threshold the researchers applied.

Meanwhile, the EU decided in 2023 not to approve d-allethrin as an active ingredient in insecticides targeting mosquitoes and other insects.

The decision was based on findings that substances formed when allethrin breaks down after light exposure may damage genetic material, and that the compound could also harm the environment, including water and soil. The EU concluded at the time that safe conditions of use could not be established given the risks to human health and the environment.

South Korea's Ministry of Environment — now the Ministry of Climate, Environment and Energy — said after the EU decision that it would re-examine the safety of allethrin. The ministry said it believed the scientific methodology the EU used to assess allethrin's risks had limitations, and that it would conduct additional verification through specialist institutions including the National Institute of Environmental Research.

woo@heraldcorp.com