Sunscreen And Insect Repellent: Which One, When, And How Often?

Next week is March break for many students here in Canada, and many of us who live in cold climates will be escaping to warmer destinations.  The spread of chikungunya, and more recently of zika virus, have made many of us more aware of the need to prevent mosquito bites when travelling to destinations where these diseases are endemic.  When visiting areas of risk, it is clear that we need to protect ourselves and our loved ones both from insect bites and from excessive sun exposure. This post addresses the question of how to safely do both.

How Should I Choose a Sunscreen?

I've written at length on how to use sunscreen, how to choose a sunscreen, and the link between sun exposure and skin cancer.  In brief, when in a warm climate, one should choose a "broad-spectrum" sunscreen with an SPF of 30 or higher.  Sunscreen should be applied liberally; 1/2 teaspoonful should be applied to the face and neck and 2-3 ounces (a shot glassful) should be used when applying sunscreen to the entire body.  Re-application should be done every 2-3 hours, and more frequently when sweating or immersed in water. 

How Should I Choose an Insect Repellent Product?

Insect repellents are available with many active ingredients and in many formulations.  Most insect repellents contain DEET, a chemical that has been used for 50 years and is felt to be the most effective active ingredient for preventing insect bites. Commercially-available products contain between 4 and 100% DEET, with most products on the market containing up to 40%. The CDC also recommends the use of products that contain such active ingredients as picairdin, oil of lemon eucalyptus, and IR3535.

The duration of action (the length of time that an insect repellent will be effective) of DEET-containing insect repellents depends on the concentration of this active ingredient; products that contain 10% DEET last for 3 hours, products that contain 15% DEET last for 5 hours, and those that contain 30% last for 6 hours.  Many insect repellents on the market recommend re-application no sooner than every 6 hours. When in an area where the risk of mosquito-borne disease is a concern, the CDC recommends using a product that contains 20% or more DEET.  

What Should I Choose For My Children?

The American Academy of Paediatrics endorses the use of DEET in infants older than two months, recommending that products containing up to 30% DEET be used only once per day in children.  Health Canada recommends concentrations of no more than 10% up to once per day in children 6 months - 2 years, 10% up to 3 times per day in children 2-12 years, and concentrations of up to 30% for children older than 12. For more information on these recommendations see here.

Is It OK to Combine/Layer Sunscreen and Insect Repellent?

Combination sunscreen/insect repellent products exist on the market for convenience.  There are a number of issues that come up when using these products.  Firstly, sunscreen must be applied liberally in order to provide adequate sun protection; the same is not true for insect repellent.  This means that if one applies a combination product liberally (as sunscreen must be applied), one uses more than the recommended amount of insect repellent. Sunscreen also needs to be reapplied more frequently, typically every two hours, while insect repellent may only need to be reapplied at 6 hour intervals.

Some studies have also shown that applying some sunscreen ingredients at the same time as insect repellents that contain DEET may result in both types of chemicals being absorbed in higher levels than would occur if they were used separately. Another study also showed a reduction in SPF when sunscreen and insect repellent were applied at the same time. These issues can be minimized or largely prevented by applying sunscreen first, allowing it to set for 15 minutes, and then applying insect repellent overtop.  Sunscreen can then be reapplied 2-3 hours later.

The Bottom Line: How to Protect Yourself From Both Sun Exposure and Insect Bites

1. Protect your skin from excessive sun exposure by generously apply a "broad-spectrum" sunscreen with an SPF of 30 or higher to all exposed skin.  Use sun-protective clothing, "rash guards", hats and sunglasses.

3. Apply sunscreen 15 minutes before heading outdoors.  Wait for it to dry for 15 minutes and then apply insect repellent. Sunscreen can then be reapplied when needed (usually 2-3 hours later or after exposure to water).  Insect repellents are applied far less often.

4. Apply insect repellent to exposed skin or on top of clothing.  Do not applying underneath clothing or on open wounds. Avoid applying to the hands of young children who might put their hands in their mouth or eyes.  Wash insect repellent off when it is no longer needed.

4. Adults traveling in an area where mosquito-borne diseases are a concern, might consider choosing a product that contains 20% or more DEET.  

5. Use long sleeves, pants and socks/shoes to protect your skin in the evenings.  

For more information on mosquito-borne diseases and how to protect yourself, visit the CDC's website.

 

Michelle Levy

Dr. Michelle Levy is a board-certified dermatologist specializing in medical and aesthetic dermatology. A graduate of the University of Toronto's Faculty of Medicine, Dr. Levy provides a full spectrum of dermatologic services in Toronto, Canada. Education: M.D., University of Toronto, 1999 Residency in Dermatology, University of Toronto, 1999-2004 Employment History: Self-employed, North York, Ontario, 2005-Present Medcan. Consultant Dermatologist. 2007-Present