Repelling mosquitoes: A guide to what works and what doesn't

A mosquito acquires a blood meal from a human at the Center for Disease Control in Atlanta in 2006. (Center for Disease Control and Prevention / James Gathany)

Getting covered head-to-toe in mosquito bites seems to be as much a part of Canadian summers as sunburns, black flies and scorched burgers.

And Canadians have been known to try anything to fend off the tiny blood-suckers, from smoke coils, to candles, to garlic pills.

For the longest time, the only really reliable weapon in Canadians’ skeeter-fighting arsenal was DEET. The insect repellent has been around for 50 years and remains one of the best weapons against mosquitoes, offering excellent bite protection that lasts for hours.

But DEET – an oil formally called N,N-diethyl-meta-toluamide -- isn’t perfect and many have had bad reactions while using it.

Still, the number of repellent choices has grown in recent years, with several new mosquito-fighting options entering the market.

So which of these new products actually work and how do they stack up against what’s already out there? Let’s take a look at a few.

Icaridin: This is a new repellent that entered the U.S. market in 2005 (as “picaridin”) and was approved by Health Canada in 2012.

Studies have found Icaridin can work as well as DEET, offering several hours of bug protection. But unlike DEET, Icaridin is odourless and much less likely to cause skin irritation and sudden reactions, such as nausea. It also isn’t greasy and does not ruin plastics or synthetic fabrics the way DEET can.

The repellent is so effective, the World Health Organization recommends Icaridin, alongside DEET and another repellent called IR3535, as one of the best choices for preventing mosquito bites that can lead to disease.

In Canada, there are still only a few products that contain Icaridin, but look for it in bug-spray products that promise a “clean” or “dry” feel.

Oil of lemon eucalyptus: When the oil of this Australian plant is refined into a substance known as p-menthane-3, 8-diol, or PMD, it becomes an effective repellent that helps ward off mosquitoes.

It’s currently found in the Off! Familycare Botanicals line, as well as under the Repel Natural and Cutter brands.

While PMD is considered as effective as DEET with a much more pleasant scent, its protection wanes after about two hours -- less than the four to six hours of protection offered by products with 30 per cent DEET.

And repellents with oil of lemon eucalyptus can also cause skin and eye irritation in some, so Health Canada and the CDC recommend that PMD not be used on children under three years of age.

Clip-on repellents: These are fairly new on the market and contain a fan that blows a vapour of an insecticide called metofluthrin.

Consumer Reports tested OFF! Clip-ons and found that while the products promised 11 hours of protection, they stopped preventing bug bites after about two hours.

There have also been concerns about the safety of metofluthrin-emanating devices. Health Canada reports that within the first year of clip-ons entering the market, its Pest Management Regulatory Agency received six reports of people feeling ill after using them. These incidents involved everything from dizziness and irregular heart rate, to muscular weakness and loss of consciousness. The agency says it’s continuing to monitor incidents involving the devices.

Mosquito lamps and lanterns: These devices use butane heaters or candles to warm up pads containing the insecticide allethrin -- the same chemical used in most mosquito coils.

The products claim to offer up to 15 feet of odourless bug protection, but their effectiveness drops when there’s a breeze.

The product label warns against directly breathing in the vapours, and there have been a number of incidents reported in Canada and the U.S. involving breathing problems and skin irritations from people using the lanterns.

Permethrin is an insect repellant that is sprayed onto clothing, mosquito netting and tents rather than skin. It can repel mosquitoes for several hours and even through several washings. But it is not currently available in Canada as a repellent.

OTHER OPTIONS

Citronella candles or torches: Studies have shown that candles or torches containing citronella oil can somewhat help ward off mosquitoes because the smoke can confuse the bugs and prevent them from smelling you.

But studies also shown that their range of effectiveness is small -- less than 2 metres, assuming there’s no breeze.

As well, the candles produce large particles in their smoke and there have been concerns about how safe it is to regularly breathe in this smoke.

Mosquito coils: Like citronella candles, mosquito coils produce a smoke that confuses mosquitoes. The coils contain the insecticide allethrin. But once again, their range is limited and they don’t work well when there is a strong breeze.

More worrying, though, is a number of recent studies that show the smoke can be toxic to the lungs, especially when they are used indoors -- as they often are in South Asia. One study found that burning one mosquito coil would release the same amount of large particulates as that released from 100 cigarettes, and as much formaldehyde as 51 cigarettes.

Essential oils: Plant-based botanical oils, such as clove oil and citronella oil, can offer some protection against mosquito bites. But studies have found the protection lasts only a matter of minutes; the authors of one study say the oils should not be relied on to provide protection in areas where mosquito-borne diseases are a substantial threat

WHAT DOESN’T WORK

Citrosa geraniums, also called mosquito plants: These plants are often sold as mosquito repellents, with some claiming that the leaves emit a smell that keeps the pesky bugs at bay. But several studies have shown they are useless in warding off mosquitoes, with one study finding they were about as effective as doing nothing at all.

Bug zappers: Electric insect traps, or bug zappers, as most of us call them, are useless for two reasons. First, studies have shown they fail to attract mosquitoes. Second, they are indiscriminate in their killing. Studies have shown that bug zappers kill thousands of bugs that are perfectly harmless and necessary to the ecosystem, such as moths and fireflies. In fact, one study found that of the thousands of insects these bug zappers kill, less than one per cent were biting insects. The authors of that study went so far as to say that using bug zappers should be considered ”irresponsible.”

Eating garlic or vitamin B12: Sorry to those looking to pop a pill to ward off skeeters: Several studies, including the so-called “gold standard” of studies -- the double blind, randomized control trial -- have shown that neither garlic nor B12 have any impact on mosquito bites.