A. Although protecting you and your loved ones from both sun damage and insect bites with one product sounds convenient (anyone with squirmy small children wishes for that), it is better to use two different products.
Sunscreens and insect repellents are both effective and safe when used separately, but if combined, problems can arise. Certain sunscreen formulations decrease in their ability to screen out ultraviolet (UV) radiation when used with DEET (N,N-Diethyl-m-toluamide), the most effective and common bug repellent. In some studies, the combination led to a more than 30 percent reduction in SPF. What’s more, sunscreens enhance absorption of DEET into the skin, potentially increasing toxicity — especially in children.
The problem is compounded by the application directions. You should apply sunscreens generously and frequently: That means one ounce of sunscreen to the entire body at least every two hours — and more often if you’re swimming or sweating. You should only apply insect repellents, though, every two to six hours, depending on the concentration, and you should avoid applying it to the face. It is difficult to reconcile the opposing requirements of combination formulations.
In summary, I advise you to use two separate products. Apply sunscreen first, then an insect repellent, following the manufacturer’s instructions for each.
About the Expert:
Pierre George, MD, practices general dermatology and Mohs surgery at Dermatology Consultants in St. Paul, Minnesota. He is the author of numerous articles and is a fellow of the American Academy of Dermatology, the American Society for Mohs Surgery and the American Society for Dermatologic Surgery.