Mosquito Repellents

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Mosquitoes are initially attracted to the carbon dioxide (CO₂) that is exhaled by humans and other animals. The female blood-feeding mosquito will fly towards the source of the CO₂ and, once in close range, the mosquito detects body heat and finally sees the host. Other factors, such as body odour, may play a role in mosquito host selection. Body odor is a result of body chemistry, perfumes, shampoos, soaps, lotions, etc. One way to prevent mosquitoes from biting is to apply a mosquito repellent, preferably containing DEET (chemically known as N,N-diethyl-m-toluamide).

Why DEET?

DEET has been on the market for over 40 years. It is the most studied and effective insect repellent commercially available.

Is DEET safe?

Products containing DEET are very safe when used according to their directions. Many scientific studies have been carried out to ensure that DEET is a safe product for public use. As with chemical exposure in general, pregnant women should limit exposure to repellents. Although recent studies have shown that DEET accumulation in the fetus is low and that use is safe in later stages of pregnancy (2nd - 3rd trimester), non-chemical preventative measures should be considered. There is no indication that there is a hazard to the nursing child associated with the use of DEET by lactating women.

What percentage of DEET is needed to provide protection?

Ensure you choose the correct DEET-containing product that is suitable for the age of the person and for the time spent outdoors. A higher percentage of DEET should be applied when outdoors for an extended period of time. Lower percentages of DEET should be applied when outdoor mosquito exposure is minimal. Concentrations of DEET greater than 30% are unnecessary and not recommended. Lower concentrations of DEET are as effective as higher concentrations but do not provide protection for as long a period of time.

How do I know how much DEET is in the repellent?

DEET concentrations can be found on the label of the repellent, on the instructions under “GUARANTEE”.

DEET & Sunscreen

Products containing both DEET and sunscreen are not recommended because of the incompatible label instructions regarding methods of application. Insect repellents should be applied sparingly while sunscreens should be applied liberally and frequently. Applying both DEET and sunscreen as separate products may reduce the effectiveness of the sunscreen. If using both a sunscreen and an insect repellent, apply the sunscreen 20 minutes before outdoor activities followed by the repellent just before going outdoors.

Are non-DEET repellents effective?

There are many mosquito repellents commercially available that do not contain DEET.

These products may provide some protection from mosquito bites; however, studies have suggested that they do not provide as much protection as DEET. Additionally, repellents that do not contain DEET do not last as long as protections containing DEET.

Comparison of DEET and non-DEET Skin Applied Insect Repellents

Source: Health Canada

ALWAYS FOLLOW PRODUCT INSTRUCTIONS FOR APPLICATION

Tips for Using Mosquito Repellents

• Always follow the recommendations for application and frequency appearing on the product label.
• Check for sensitivity – apply repellent to a small area of skin on the arm and wait 24 hours before use.
• Use enough repellent to cover exposed skin or clothing. It is not necessary to apply repellent to skin that is under clothing. Heavy application is not necessary to achieve protection.
• When applying repellent, avoid cuts, open wounds, areas of skin irritation, or sunburned areas.
• Sweating, perspiration or getting wet may mean that you need to re-apply more frequently.
• After returning indoors, always wash treated skin with soap and water.
• Always apply repellent in a well-ventilated area.
• Do not use near food.
• Do not spray products directly on face. Apply product to hands and rub them carefully on face avoiding eyes and mouth.
• If you get repellent in eyes immediately rinse eyes out with water.

Applying Repellents to Children

• Ensure you choose the correct DEET-containing product suitable for the age of the child and for the time spent outdoors (see chart above).
• Do not allow children to apply mosquito repellent themselves; have an adult do it for them. Keep repellents out of the reach of children.
• When using a repellent on a child, put repellent on your hands and apply it to the child. Avoid the mouth, eyes and apply sparingly to areas around the ears.
• Do not apply repellent to children’s hands (children tend to put their hands in their mouths).
• Wash all treated skin with soap and water after returning indoors.
• It is unnecessary to apply repellent underneath clothing. Repellent can be applied directly on clothing (according to instructions on product). If repellent is applied directly to clothing, ensure clothing is washed before wearing again.
• If you suspect that your child is reacting to an insect repellent, stop using the product immediately, wash the treated skin and seek medical attention. When you go to the doctor, take the product container with you.

How else can I avoid getting bitten by mosquitoes?

Non-chemical solutions are available to protect against mosquito bites. One such product is mosquito clothing. Products, such as mosquito pants and jackets, are commercially available and if used according to instructions provide protection from mosquito bites.

• Citronella and other plants. The citronella plant has been marketed as being able to repel mosquitoes through the continuous release of citronella oils. The plant should be squeezed periodically during your outdoor event to release the oils. Under testing conditions, these plants offered no protection against bites. Also listed as natural mosquito deterrents are scented geraniums, lemon thyme, lemon balm, citronella grass, tomatoes, sweet basil, and marigolds. Remember that tall plants, grasses, weeds, and shrubs can make cozy homes for mosquitoes as well.
• Coils and candles have been touted as effective ways to repel mosquitoes from the back yard. They only work sporadically and when there is no wind. A recent study using citronella candles and ordinary candles demonstrated that persons sitting near the citronella candles had 42% fewer bites than those people with no protection; however, the use of ordinary candles also reduced the number of bites by 23%. The smoking coil contains pesticide and repels insects that venture into the smoke. Coils and candles should not be used near food.
• Bug zappers and sonic/ultra sonic repellers. These electronic devices tend to attract all types of insects and kill more beneficial or harmless flying insects, like moths and butterflies, than actual mosquitoes.

The best way to avoid mosquito bites is to stay indoors during times when mosquitoes are most active. Covering up with lightly coloured long-sleeved shirts and pants as well as socks when mosquitoes are most active is the easiest form of personal protection. If a repellent is to be used, ensure you choose a product that meets your needs. If you plan to be outdoors for a short period of time, choose a product with a lower concentration of repellent.

Sources: Health Canada, Ontario Ministry of Health and Long Term Care, Centers for Disease Control