Does Sunscreen with SPF 100 Offer the Most Protection?

Bigger isn't always better—especially when it comes to the SPF level of your sunscreen. You may be tempted to extend your outdoor time by choosing the highest sun protection factor you can find, but there's more to protecting your skin—and your family's—than numbers.

Understanding the Differences Between UVA and UVB

Outside, you're exposed to both UVA and UVB rays; the latter cause sunburn and skin cancer, which sunscreen helps prevent. "SPF depicts how long a sunscreen will protect you from burning UVB exposure," says Dr. Carolyn Jacob of Chicago Cosmetic Surgery and Dermatology. "It indicates how much longer skin will take to redden from UVB compared to without the sunscreen." (The specific time skin takes to burn varies by person, so SPF shouldn't be mistaken for the minutes or hours you can stay in the sun after applying.) "UVA rays penetrate further and also cause cancer," says Dr. Jacob. "Not all chemical sunscreens will truly protect against UVA." For that, you'll need a broad spectrum sunscreen.

Higher SPF Counts

In the United States, SPF can be as high as 100, says Dr. Jacob. "However, 100 is not double the protection of an SPF 50, so it can be very confusing." According to the American Cancer Society's website, "SPF 15 sunscreens filter out about 93 percent of UVB rays, while SPF 30 sunscreens filter out about 97 percent, SPF 50 sunscreens about 98 percent, and SPF 100 about 99 percent." This means if your beach bag contains a different SPF for each member of your family—100 for you, 50 for the kids, 30 for your partner—the protection only changes by one or two percent. SPF numbers also don't build on each other—if you apply 30 and 45, you aren't wearing 75—and products SPF 15 are rated only to stop sunburn, not skin cancer or aging; Dr. Jacob recommends a minimum of SPF 30 for everyone.

Application and Reapplication

More important than the SPF number, notes Dr. Jacob, are the sunscreen's specific ingredients. "The best ingredients to look for are zinc oxide and titanium dioxide, because they are chemical-free, physical blockers," she says. "With fair skin, it is best to use zinc oxide to protect the skin cells from DNA mutating UVA and UVB rays. Also, because you tend to see them when applying, you are less likely to have skipped an area." When applying the sunscreen, it's critical to use enough—one ounce each time, about two tablespoons—and reapply regularly. "You have to make sure you are actually applying enough," says Dr. Jacob, "and they still need to be reapplied every 90 minutes, or after swimming or sweating." In addition to sunscreen, she recommends other sun protection efforts: staying in the shade, planning your time outside for before 10 a.m. or after 4 p.m. to skip the sunniest part of the day, and wearing clothing with UPF protection.