Still, these studies have led some people to choose physical sunscreens over chemical ones.
“I have a tendency to opt for the natural stuff, the physical sunscreens,” Friedman says, “but overall, the positives outweigh the negatives for all sunscreens” by reducing skin cancer and aging risks.
In addition, the negatives aren’t limited to chemical sunscreens. The titanium dioxide in many physical sunscreens also degrades in light and can generate free radicals in the skin.
What’s the best way to avoid the negatives? According to Hanson, the key is to use sunscreen properly, so it doesn’t degrade in the sunlight.
“It all comes back to the need to reapply,” she says. Most sunbathers don’t reapply their sunscreen, or they apply it too infrequently. Hanson urges anyone venturing into the sunshine to follow the Skin Cancer Foundation’s guidelines, which call for one ounce (about two tablespoons) of sunscreen for an adult’s entire body, reapplied every two to three hours. The reapplications replace light-degraded sunscreen, preventing some of the free radical formation and more consistently protecting the skin, Hanson says.
Both the Skin Cancer Foundation and the American Academy of Pediatrics recommend that babies younger than 6 months of age be kept out of the sun and receive only very small amounts of sunscreen when sun exposure can’t be avoided. They say that infants’ skin is more likely to absorb or react to the ingredients in sunscreens.
When shopping for sunscreen, Hanson suggests seeking out brands that contain antioxidants such as Vitamin E (often listed as Vitamin E acetate) or Vitamin C (often listed as sodium ascorbyl phosphate), which are added to many physical and chemical sunscreen formulations to counteract free radical formation.
“Look for sunscreens that have antioxidants highest up on the list of ingredients,” she says, “as that means they have a higher antioxidant content.”
What about SPF? SPF, or sun protection factor, is a number that denotes how effectively a sunscreen will protect your skin from UVB rays. (It doesn’t measure UVA protection.) The higher the number, the longer lasting the protection, no matter what type of sunscreen it is. An SPF of 15, for example, roughly means it will take you 15 times as long to develop a sunburn as it would without wearing sunscreen.
Sheu, Friedman and Hanson agree that an SPF of around 30 is the magic number. Sunscreens with higher SPFs can create a false sense of security and lead users to stay in the sun too long.
Do higher SPFs mean more potentially worrisome chemicals in the sunblock? Higher SPF means a sunscreen has a higher concentration of a given UV-filtering ingredient, or more UV filters mixed together; those are the two ways you get the high SPF.
Whatever you choose and however you use it, any sunscreen is better than none at all, Friedman says. “The bottom line is there’s an unequivocal, worldwide rise in the incidence of melanoma, the deadliest form of skin cancer,” he says. “So the most important thing we can do is protect ourselves from the sun.”