Myths and facts about mosquito bites

Everything families need to know about bug bites, insect repellent and DEET.
Photo: iStockphoto

Photo: iStockphoto

With bug season upon us, it’s a good time to review the best ways to avoid bites without using chemicals (as well as the guidelines for safer use of insect repellent, when it’s needed). In order to debunk myths about mosquitoes and get the facts straight, I asked mosquito expert Cameron Webb, a medical entomologist of the University of Sydney, in Australia, to share tips for avoiding these pests this summer.

How can my family avoid mosquito bites this summer?

The Canadian Paediatric Society (CPS) recommends the following to minimize those itchy bites:

Don’t let them breed
Mosquitoes breed in standing water. One of the most effective ways to decrease mosquitoes is to get rid of standing water by emptying kiddie pools, planters and toys that collect water.

Avoid hot spots
Avoid areas with large populations of mosquitoes, and avoid being out at times when mosquitoes are most active—like dusk and dawn. Keep your window screens in good repair and doors closed to keep mosquitoes out. Mosquitoes like to hide in tall grass, so avoid those areas and keep your grass well cut. Strong house fans used outside on a patio or deck can also help to keep the little buggers away. Webb explains that the reason for this is twofold: First, mosquitoes don’t like to fly in a breeze; second, fans help to blow away the CO2 we exhale, making us less detectable to mosquitoes.

Create a barrier
Dress your child in light-coloured, loose, long-sleeved shirts tucked into long pants, and pants tucked into socks. Wear full-coverage shoes like running shoes and avoid sandals. Net covers for strollers can help to create a barrier between babies and bugs; look for the kind that have protection against ultraviolet rays and bugs for a double-whammy of protection.

If you must, use bug spray
According to Webb, mosquito repellent is the most effective way to avoid mosquito bites. Health Canada’s Pest Management Regulatory Agency has approved DEET, picaridin/icaridin (up to 20%), 10% oil of lemon eucalyptus and 2% soybean oil for use in Canada. The CPS recommends that children should only be exposed to small amounts of insect repellent chemicals like DEET (read more on DEET and alternatives below).

Are there health risks associated with mosquito bites?
Mosquitoes, and in particular the viruses and parasites they transmit, actually account for more deaths in humans per year than any other animal or insect. It is estimated that as many as one-million people around the world die each year due to mosquito-related illnesses like malaria and Dengue fever. While these diseases are rarely seen in North America (apart from in travelers who have gone abroad), North American mosquitoes do carry a number of pathogens—the most commonly transmitted is West Nile virus (WNV). WNV was first seen in New York in 1999, and subsequently in Canada in 2002. It mainly affects young children and older adults. While many infected individuals do not show any symptoms, about 20% of infected individuals will develop a fever, headache, muscle aches and fatigue 14 days after a bite. The illness typically lasts three to six days. Approximately one in 150 people will acquire more serious illnesses associated with WNV, including brain infections like encephalitis or meningitis.

Some children also have allergic reactions to mosquito bites, or scratch bug bites to the point of breaking skin, which can lead to secondary skin infections, sometimes requiring antibiotics.

Why do some people seem to be more attractive to insects?
There are many old wives’ tales about diet and mosquitoes, like the myth that eating salty foods like pretzels or chips or potassium-rich foods like bananas or avocados increases your attractiveness to mosquitoes. “There is no evidence that anything you eat or drink will significantly change how attractive you are to a hungry mosquito,” says Webb. He acknowledges that some people are more appealing to mosquitoes than others, but the exact reason why is unclear; “Most likely, it comes down to the cocktail of chemicals and microbes on our skin,” he says. “This mix of hundreds of compounds influences if we’re likely to be bitten by more mosquitoes than our friends.” Research shows that mosquitoes are highly attracted to CO2, the gas we blow off when we exhale. They are also attracted to lactic acid, which is released when we sweat. So people doing physical activity with increased rate of breathing and sweating are especially attractive to mosquitoes.

How much DEET is safe for kids?
The CPS recommends limited use of DEET, only when needed, to protect against mosquitoes, flies and ticks. DEET containing bug repellent should not be used on infants six months of age and younger, and should only be applied to exposed skin (not be sprayed under clothing). Here’s what CPS recommends age by age:

  • Six months to two years (only when mosquito bite risk is high): up to 10% DEET, not to exceed one time per day
  • Two years to 12 years: up to 10% DEET, not to exceed three times per day
  • Older than 12 years: up to 30% DEET

DEET has been studied extensively with only very rare instances of adverse side effects (like brain damage) that tend to occur with excessive use. More commonly, some children may find DEET irritating to their skin, causing itchiness or rash. It is important to read the label, use DEET sparingly and according the CPS guidelines, and balance the risk of reactions to mosquitoes bites with concerns of rare cases of potential toxicity.

What does the percentage of DEET mean?
“Keep in mind that the strength of a repellent doesn’t determine how many mosquitoes are stopped from biting; it determines how long a repellent provides protection from biting,” says Webb. A 30% DEET formulation, only recommended for children 12 years and older and adults, protects for five to eight hours, whereas a 10% DEET formulation, approved for children older than six months, can last two and a half to four and a half hours. A 5% DEET formulation can protect you just as well as 10% or 30%, but only for approximately two hours (so for an hour soccer game at dusk, 5% may do the trick). “Over short periods of time, any repellent, regardless of how low or high the dose, will keep away the same quantity of mosquitoes if applied correctly,” says Webb. 

Are there non-DEET or natural alternatives?
Health Canada has approved the use of up to 20% of picaridin/icaridin, a non-DEET alternative for safe use in children to protect against mosquito and tick bites.

Also, 10% oil of lemon eucalyptus (p-menthane 3,8 diol) (PMD) is approved for use in children older than three years of age by Health Canada and the CPS, up to two times per day. It is sometimes referred to as a “natural” option, as it is derived from an Australian plant, Corymbia citriodora, but Webb cautions that it’s still a chemical repellent. “The product is not an essential oil as such, it is the by-product of a distillation process.” It is effective for up to two hours against mosquitoes and five hours against black flies.

There are a variety of other options such as 2% soybean oil. However, Webb says they may not work as well to protect children from bites. The CPS cautions that just because a label says “natural” does not mean it is safe for use in children. The effectiveness and safety of these products may not be known, and may not protect against other insects, like ticks.

What are the safest ways to use insect repellent?
The CPS recommends these safety guidelines:

  • Read the whole label carefully prior to using.
  • Insect repellent should always be applied by a grown-up and should be kept out of reach of children.
  • Insect repellent should only be sprayed or applied outdoors and not in enclosed spaces, like a cottage or tent.
  • Never spray insect repellent near food.
  • Only apply to exposed skin.
  • Do not spray or apply insect repellent under clothing.
  • Avoid the eyes and mouth. Do not spray directly on the face, apply to your hands and then apply with your hands to the child’s face. If repellent gets in the eyes, rinse immediately with water and follow further instructions on the label.
  • Do not apply to children’s hands, as they may rub their eyes or put their hands in their mouth.
  • Do not apply over open wounds, cuts or scrapes, rashes, sunburned or irritated skin.
  • Follow the guidelines for the percentage and number of applications allowed for your child’s age, and use sparingly.
  • Wash off with soap and water as soon as you come indoors and no longer need protection.
  • If your child has a suspected reaction to a product, wash area exposed immediately with water, seek immediate medical attention and bring the product with the child to the doctor. 

What’s best for kids: Aerosol sprays, spray pumps, lotions or wipes?
Children often squirm when applying sprays and this could put them at risk of inhaling it or getting it in their eyes. But according to Webb, as far as effectiveness, the formulation doesn’t really matter. “However, as repellents must be applied evenly to all exposed areas of skin, a formulation should be chosen that makes that job as easy as possible,” he says. “I usually recommend lotion or creams as they can easily be applied to the hands of caregivers and then to children.” Sprays should also be applied to the hands of an adult and then applied evenly to the child’s skin. “Children shouldn’t be allowed to apply repellent themselves,” says Webb.

Are insect repellents/sunscreen combination lotions recommended?
Combinations of insect repellent and sunscreen are not approved for use in Canada. The main problems with combos is that their application recommendations don’t match up, says Webb. Sunscreen should be applied 20 to 30 minutes before going in the sun and should be reapplied at least every two hours, and sometimes more if sweating or swimming. Insect repellent, on the other hand, should be used only in small amounts and less frequently, with specific guidelines for limited reapplication by age.

This article was originally published July 2014.

Joelene Huber is an assistant professor of paediatrics at the University of Toronto and works at the Hospital for Sick Children, specializing in development and autism spectrum disorders. She is a regular on television news programs and mom to two small children. Follow her on Twitter at @DrJoeleneHuber

Read more:
Outsmarting mosquitoes
Ticks: 6 things your child needs for proper protection
Deer ticks in Canada: Everything you need to know

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