Bzzzzz’ slap! Ah, the sounds of summer. Enjoying the Canadian outdoors often means finding ways to keep bugs from biting. But with so many insect repellents on store shelves, how do you find one that works? ‘Different people have different levels of attraction for biting insects,’ notes Fiona Hunter, a medical entomologist at Brock University in St. Catharines, Ont. It has to do with factors such as the amount of carbon dioxide you exhale (these bugs love carbon dioxide) and the microscopic organisms on your skin, as these give off different ‘scents’ to a bug. By interfering with these factors, a good repellent will confuse or turn off those suckers looking for blood. But some products do work better than others, regardless of how much you may be naturally attracting bugs.
Bug repellents containing DEET
The chemical compound DEET, or N,N-diethyl-meta-toluamide, has been used in insect repellents for more than 50 years, and for good reason: It’s still the most effective and longest-lasting product available. It’s not fully understood how it works. Some scientists believe it jams the insect’s ability to track a human, but in 2008 entomologists at the University of California proved mosquitoes actually smell and avoid this compound.
DEET has a bad rap, though, because it has had reports of toxic effects when used at high concentrations or ingested. But Health Canada has deemed it safe when the concentration is 30 percent or less and it’s used as directed on the label (30 percent is the highest concentration legally allowed for sale in Canada). ‘You have to weigh your risk versus benefit,’ says Nancy Kleiman, a pharmacist and instructor of pharmacy practice at the University of Manitoba, where mosquitoes are the focus of ongoing research. ‘DEET can protect you from the West Nile virus,’ she says. A product containing up to 30 percent DEET usually lasts for six hours, and up to 10 percent (recommended for kids age six months to 12 years) can last three hours. But DEET shouldn’t be used on babies younger than six months.
Don’t mix sunscreen and DEET‘Canadian researchers have shown that oxybenzone, a common sunscreen ingredient, will increase the absorption of DEET into the skin. ‘Anything intended for topical use only shouldn’t be going into the body,’ says Xiaochen Gu, a professor at the University of Manitoba’s faculty of pharmacy, who led the study.
If you’re going to use a DEET product, he says you can avoid this penetration effect by applying repellent at least 30 minutes after sunscreen, and using a DEET spray instead of a lotion. ‘When you rub in the lotion, basically you force the molecules into the skin,’ he notes.
Controlling bugs with botanical bug repellents
Those who want to avoid DEET can look for plant-based products in drugstores, health stores and online. In Canada, the two most common botanicals registered as insect repellents are citronella and soybean oils. Citronella sprays and lotions won’t last more than 30 minutes to two hours, which could be inconvenient on a long hike in the woods. ‘If you’ve only got about an hour’s worth of protection, you’ve got to keep reapplying,’ notes Kleiman, ‘and most people don’t take the time to do that.’
Just because a product is from a natural source, though, doesn’t mean it can be used liberally. Some citronella product labels, for example, limit the number of times you can apply it in a day. Citronella products may cause skin reactions in certain people and are not recommended for use on babies or toddlers. Soybean oil, though, is considered safe for all ages; it can block mosquitoes for 3’1/2 hours and black flies for up to eight.
Other plant-based formulations such as geranium and lavender oils aren’t approved in Canada as bug repellents, so products containing these ingredients can’t be marketed as repellents. Kleiman adds that for people with skin sensitivities, natural products may be a bother: ‘A lot of the alternative ones have perfumes and additives in them.’
Bug repellent product advancements
Two chemicals, icaridin (picaridin) and IR3535, are currently in wide use in the U.S. as non-DEET repellents (both are used in Avon’s Skin So Soft Bug Guard products, for example), although neither is approved yet in Canada. Last year, Gu published his findings that picaridin does not soak into the skin the way DEET does when used with sunscreen. ‘There are some good things there,’ he says, ‘but picaridin is quite new and it will take some time for the general public to accept it.’
Another chemical, permethrin, repels bugs but it’s also an insecticide, so it’s not approved for skin application. It can be used on mosquito tents or fabrics. ‘Permethrin protects you because they’re not biting through clothing,’ says Hunter, but it’s not fail-safe: ‘Your bare hands and face are still prone to bites.’ The Canadian government has approved two permethrin products for fabrics, but so far they’re restricted to use by our military.
Cream vs. spray repellents
Although not everyone likes the feeling of cream, at least you can control where it’s going. ‘Sprays are notorious for not being put on evenly,’ says Kleiman. Plus, they can be accidentally inhaled, especially if you apply them indoors. But a spray can be used on both your clothes and your skin, increasing your protection. Reapply a product when necessary (check the label), or if you’ve been swimming or sweating.
For people who don’t want stuff on their skin, there are candles, coils and lamps that release repellent, and they do help (although avoid inhaling them). But because they’re only near you and not on you, they won’t do the whole job. Bottom line: ‘Application right on your skin is the most effective,’ says Hunter.
This article was originally titled "The Buzz on Repellents," in the Summer 2010 issue of Best Health. Subscribe today to get the full Best Health experience’and never miss an issue!’and make sure to check out what’s new in the latest issue of Best Health.