Mosquito coils: A summer necessity or backyard health hazard?

Summer is a time spent outdoors with your friends, the barbecue, and nature – and all the good and bad that entails!

Summer time is also mosquito season. Mosquitos and their red, itchy bites are at best, a nuisance. At worst, they are a health risk – vectors for potentially lethal diseases like dengue and malaria.

The mosquito coil is a common solution. Light it up and watch the little pests drop mid-flight! But in an effort to protect our health from mosquito-borne pathogens, are we actually risking it with mosquito coils? Let’s find out!

What are mosquito coils?

Following the ancient method of burning aromatic plants to drive insects away, the earliest mosquito coils were made with pyrethrum, a substance extracted from chrysanthemum flowers with mosquito-repelling properties.

Modern mosquito coils work by killing or incapacitating mosquitos (via pyrethroid insecticides) or repelling them from the area (via aromatic substances like citronella). Mosquito coils contain these substances as well as other chemicals that give the coil its shape and lengthen burning time. No matter their composition, studies have shown that mosquito coils are effective in reducing the likelihood of getting bitten.

The problem begins when these chemicals are released into the air when we burn mosquito coils. We breathe them into our lungs, and the chemicals enter our bloodstream, causing potentially adverse effects. Here are some of the substances in mosquito coils that could have harmful effects on our health.

1. Pyrethrum

The main ingredient of mosquito coils is pyrethrum, an organic insecticide made from the extract of a variety of daisy called Chrysanthemum cinerariifolium. Pyrethrum is toxic to mosquitos; even at low doses, it’s capable of knocking down flying insects. It’s not terribly harmful to mammals, including humans, but it still poses some risks.

Pyrethrin is the active compound in pyrethrum. Inhaling pyrethrin may bring on symptoms that mimic asthma (though not related to the actual development of asthma), such as difficulty breathing, wheezing, coughing, inflammation of the airways. These symptoms are often relieved if the person leaves the area and inhales fresh air.

2. Allethrin

Allethrin is a pyrethroid, which means it’s a synthetic duplicate of pyrethrum. No longer organically drawn from chrysanthemums, allethrin is slightly to moderately toxic compared to pyrethrum.

Allethrin is a central nervous system stimulant, meaning it “ups” bodily functions. A 2008 human study showed that protective liver enzymes increased in persons chronically exposed to allethrin-based mosquito repellents, signaling that liver damage has occured. People sensitive to ragweed pollen have increased risk.

3. Aldehydes

Formaldehyde and acetaldehyde are not ingredients of mosquito coils, but they are the by-products released when the ingredients are burned. Formaldehyde and acetaldehyde can be found in pollutants like car exhaust, factory emissions, and cigarette smoke.

Firstly, formaldehyde and acetaldehyde are respiratory system irritants. Burning mosquito coils releases particulate matter in the coil smoke, sized fine and ultrafine. These are microscopic dust-like particles less than 100 nanometers in diameter.

Once inhaled, ultrafine particles penetrate and settle deep in the lungs, where they are unable to be removed by the body. Immediately, they may cause irritation or inflammation of the lungs. With long-term use, they could heighten the risk for cardiovascular and lung diseases.

Aside from affecting the respiratory system, another aldehyde produced by mosquito coils called acrolein can cause irritation to the eye.

The bigger trouble with aldehydes is that they are highly reactive. Once inside the body, they are able to react with the body’s normal cells and change their genetic makeup. Thus, they can damage DNA and encourage the development of cancers.

A 2003 research study showed that burning one mosquito coil releases enough formaldehyde to rival burning 51 cigarettes. The amount of aldehydes released by mosquito coils is six times higher than the safe limit set by the Office of Environmental Health Hazard Assessment for aldehyde concentration.

The effects are worsened if the room is small or has poor ventilation, because the fumes stay in the area for longer. They can also be harmful if you keep the coil in close proximity to you, such as by the bed when you sleep.


So are mozzie coils harmful to your health or not? Even scientists say it’s a complicated verdict to hand down. We can’t deny the convenience of mosquito coils – they’re effective, cheap, and capable of protecting a large area all at once. But we also can’t ignore the toxic substances in mosquito coils that make this possible.

For these reasons, it’s safer to use mosquito coils outdoors. They easily and efficiently repel mosquitos from your yard, and when their chemical contents are released into the open air, there’s less chance of you inhaling a large concentration of chemicals that are harmful to your health.

Indoors, you’re better off using smokeless mosquito repellent devices or natural oil diffusers. And you can protect yourself individually by applying topical insect repellents – whether you’re indoors or outdoors – and covering exposed skin.

Finally, in Australia, all mosquito-killing products are required to be registered under the Australian Pesticides and Veterinary Medicines Authority. Skip sketchy products that don’t declare their contents or lack a registration number. For your safety, only use mosquito coils that have been approved by the local authorities.

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