While both sunscreens and insect repellents are effective and safe when used separately, combining them can lead to complications. Certain sunscreen formulations may experience a decrease in their ability to block ultraviolet (UV) radiation when used with DEET (N,N-Diethyl-m-toluamide), the most common and effective insect repellent.
The Science Behind the Interaction
Studies have indicated that the combination of sunscreen and DEET can result in a significant reduction in the Sun Protection Factor (SPF). In some research, this reduction has been observed to be more than 30 percent. This issue is further complicated by the differing application guidelines for each product.
Sunscreens are designed for generous and frequent application. The general recommendation is to use one ounce of sunscreen to cover the entire body at least every two hours, with more frequent application needed if swimming or sweating. In contrast, insect repellents typically only need to be applied every two to six hours, depending on their concentration, and it is advised to avoid applying them directly to the face.
Furthermore, it has been suggested that the effectiveness of insect repellents relies partly on their scent. Masking this scent with sunscreen could potentially weaken the repellent's power. This interaction underscores why using two separate products is often the recommended approach.
According to Pierre George, MD, who practices general dermatology and Mohs surgery, there are implications in mixing these two types of products. Studies have shown that sunscreen's efficiency can drop by about 30 percent when used alongside insect repellents containing diethyltoluamide or DEET.
The Recommended Application Order
If you choose to use both sunscreen and insect repellent, there is a specific order that is advised to maximize their effectiveness and safety. The general consensus is that sunscreen should always be applied first. This allows the sunscreen adequate time to properly absorb into the skin before the insect repellent is introduced.
Before sun exposure, sunscreen of at least SPF 15 or higher should be liberally applied approximately 30 minutes beforehand to ensure it properly sinks into the skin. After the initial application of sunscreen, the insect repellent should be applied about 10 to 20 minutes later.
Ross Radusky, MD, a dermatologist and medical director, explains this by likening sunscreen to a barrier. He advises applying sunscreen first and allowing it to dry completely before applying insect repellent.
Why Combined Products May Not Be Ideal
Despite the availability of products that combine both sunscreen and insect repellent in a single bottle, they are generally not recommended. This is due to several factors, primarily related to reapplication frequency and potential toxicity.
As mentioned, sunscreen needs to be reapplied more frequently than insect repellent. Sunscreen typically requires reapplication every 2 hours, while insect repellents are often formulated to last for 6 to 8 hours. Using a combined product means you would either be over-applying the repellent to get adequate sun protection or under-applying the sunscreen for sufficient bug protection.
The Centers for Disease Control and Prevention (CDC) also advises travelers to steer clear of these combined products. This recommendation stems from the fact that sunscreen generally needs to be applied more often and in larger quantities than insect repellents.
Moreover, while insect repellents are safe when used as directed, over-applying them could potentially lead to safety concerns due to toxicity. Any product applied to the skin also carries the potential for irritation or allergic reactions.
Safe Application Practices for Insect Repellent
When using insect repellents, it is important to follow specific guidelines to ensure safety and effectiveness:
- Do not spray insect repellents directly on your face. Instead, spray the repellent onto your hands first and then gently pat it onto your face and neck.
- After returning indoors, it is recommended to wash the insect repellent off your skin with soap and water.
- Do not use insect repellents on babies under two months old.
For sun protection, the CDC advises applying a thick layer of sunscreen on all exposed areas. For hard-to-reach areas like your back and shoulders, it is helpful to get assistance from another person.
Sunscreen & bug spray toxicology safety tips
When spending time outdoors, especially during warmer months, it's important to be aware of potential risks such as sunburns, insect bites, and diseases transmitted by insects like ticks and mosquitoes. While the convenience of combo products might seem appealing, understanding the differences in application and potential interactions between sunscreen and insect repellent is crucial for maintaining both skin health and protection from insects.