Experts say not all sunscreens are the same, and with temperatures reaching record highs, you should reconsider which sunscreen you’re using. The two major types — mineral and chemical — handle the sun’s ultraviolet (UV) rays differently, and during extremely hot weather, these differences can matter. Here’s what you need to know. (Read this also | Why do dermatologists recommend applying sunscreen daily? Know its long-term benefits for skin health,
How does sunscreen work?
Mineral sunscreens contain zinc oxide or titanium dioxide. They form a barrier that reflects UV light before it penetrates the skin. Because mineral sunscreens are not absorbed, older formulations often had a greasy feel and a white color.
Dr. Jacqueline Watchmaker, a dermatologist in Scottsdale, Arizona, and spokesperson for the American Academy of Dermatology (AAD), said new formulations made with mineral nanoparticles “absorb into the skin beautifully.”
People who don’t like the thick texture of mineral sunscreens often use chemical sunscreens in creams or sprays. The ingredients form a thin protective film that absorbs UV rays and changes their structure, converting them into heat before they can penetrate the skin.
Eventually, the chemicals themselves are absorbed into the bloodstream, and health officials say more research is needed to understand the safety implications of long-term use.
When does it make a difference?
The AAD advises on its website that in general, “the best sunscreen is the one you will use over and over again.”
The group recommends using any waterproof sunscreen with a sun protection factor (SPF) of 30 or higher, which provides broad protection against both UVA rays, which cause signs of aging, and UVB rays, which cause sunburn.
But according to Watchmaker and Dr. Ross Radesky of the Dermatology Treatment & Research Center in Dallas, Texas, during peak summer, when temperatures reach 90 degrees Fahrenheit (32 degrees Celsius) or above, and humidity is high, it’s better to use a mineral sunscreen for at least a few days.
Chemical sunscreens can lose their filtering ability when exposed to extremely high temperatures.
Extreme heat means more sweating, and sweat can cause itching and rashes, which some people are prone to due to the ingredients in chemical sunscreens. The AAD advises that people with sensitive skin should opt for a mineral sunscreen even when it’s not extremely hot.
apply sunscreen more often
Habits matter, too. The AAD says many people apply only 20%–50% of the amount of sunscreen needed to achieve the SPF protection level stated on the label.
“An adult needs one ounce of sunscreen, which is about the equivalent of a glass,” Watchmaker said, which should be applied with a double layer on the most sun-exposed areas, such as the face, chest and shoulders.
The AAD says sunscreen should be applied to dry skin 15 minutes before going outdoors, and reapplied at least every two hours, and should also be applied after swimming or sweating.
Keep the sunscreen container away from heat.
A 2012 study published in the Journal of the American Academy of Dermatology found that eight hours of exposure to temperatures between 86 and 140 F (30 to 60 C) can irreversibly change the physical properties of chemical sunscreens, resulting in reduced efficacy.
If sunscreen has to be left in hot vehicles or in the sun, pack it in a cooler. You can tell if the sunscreen has been exposed to extreme heat if its components have begun to separate.
Experts caution against ordering sunscreen online in the summer, especially in hot weather, because it can spoil if left in a hot mailbox. (Reporting by Nancy Lapid; Editing by Bill Berkrot)
