Is Zika Coming to a City Near You? Get Out Your DEET!

Two viruses worry me this summer and they are carried by mosquitoes. One remains a constant worry, the West Nile virus. And the other is the Zika virus.

Both viruses cause significant harm to humans. Therefore, as we head into the summer months and travel north or south, make sure to take out the bug spray. It’s your protection from getting bitten by a mosquito that may be carrying the virus.

Mosquitoes are attracted to CO2 and lactic acid. The way a mosquito “repellent” works is not by being detected and driving insects away, but by blocking their ability to smell things that otherwise would attract them. So in essence, they ignore you.

The best substance found to block mosquitoes’ powers of detection is DEET. Its effects can last for several hours. Products with 10% to 35% DEET should be fine under most conditions. Anything over 50% is overkill, except in unusual circumstances in which insect biting pressures are truly intense, or under conditions of very high temperature and humidity such as visiting a tropical jungle.

Repellents with DEET may damage plastics (such as watch faces, eyeglasses and frames), spandex, leather, and painted surfaces, but don’t damage natural fibers (cotton, wool, or nylon). Most importantly, there is no genuine evidence that DEET is toxic. Nevertheless, I would air on the side of caution, be careful applying large doses to children.

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.


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

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.

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 these types of airborne repellents.

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. 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.


Bug zappers: These electric insect traps don’t work for one big reason; they fail to attract mosquitoes. These zappers kill thousands of bugs indiscriminately, including harmless ecosystem necessary ones such as moths and fireflies.

Essential oils: Plant-based botanical oils, such as clove oil and citronella oil, can offer some protection against mosquito bites.

How about taking garlic or Vitamin B12 as a repellent?

Sorry to those looking to pop a pill to ward off mosquitoes. Several studies, including the so-called “gold standard”, double blind studies have shown that neither garlic nor B12 have any impact on warding off mosquitos.

Garlic is only one of a list of plant compounds with similar “repellent” effects, including: citronella, cedar, verbena, geranium, lavender, pine, cinnamon, rosemary, basil, thyme, allspice, and peppermint.

All these substances have a very limited efficacy, in terms of duration, and if you are going to be exposed to mosquitoes for more than an hour or two, you should get a good DEET-based spray or lotion and stick with it.


Author: Elaine Chin

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