While lathering up with SPF is an easy and important task, there’s a lot about the process that is difficult to comprehend. For starters, what do those SPF numbers even indicate? And which one should you actually be using? They climb all the way up to 100—but is that truly necessary, especially when many brands are selling moisturizers and sunblocks with SPF 15?
We fielded these questions and more to a group of board-certified dermatologists to get some clarity on SPF and the standards we should set when buying and applying it.
As it turns out, it’s not all about the SPF number, which itself can mislead most consumers. But let’s start there:
How SPF Works
Mariana Atanasovski, M.D., has a good breakdown of SPF numbers: “SPF 30 blocks 97% of UVB rays, whereas SPF 50 blocks 98% and SPF 100 blocks 99%,” Atanasovski says. UVB rays are the ones that ‘photoage’ your skin, procuring dark spots, wrinkles, and leathery tans. Let’s pretend you’re someone who’s totally averse to any kind of tanning, or whose skin is so fair that it only burns in the sun. In that case, Atanasovski suggests investing in SPF 100. Otherwise, most of us are safe settling on SPF 50, and it’s 98% protection. If you want to tan a little, you could step down to SPF 30.
Lastly, be sure your sunscreen is labeled “broad spectrum,” which means it also blocks UVA rays—the ones that cause skin cancer. There’s less of a scale for that—generally, it blocks them or it doesn’t. So get “broad spectrum” products only, for the assurance. We like:
SPF 30 Is a Good Place to Start
Most dermatologists in our survey suggested starting with at least SPF 30, since it provides 97% coverage compared to SPF 15’s 93%. (Again, that percentage refers to the amount of UVB rays that are blocked.) You’ll still get a little tan and glow with SPF 30, which no dermatologist will ever say is a good thing. As non-dermatologists, though, we’re comfortable touting a summer tan as a positive thing—when you follow the rest of this advice and get said tan ever so gradually.
“Everyone should be using at least SPF 30 with broad spectrum coverage daily, regardless of whether or not you plan to spend dedicated time outdoors,” Dr. Audra Isaac Grossman says. This includes your daily moisturizer, even in winter. We like:
That SPF Number Is Usually Incorrect—But It’s Not the Brand’s Fault
Because of human error, we don’t typically get the SPF value that we’ve opted for. You need to liberally lather on the lotion to get all of its benefits, and reapply every 60–90 minutes, and immediately after swimming or sweating.
“Nobody in the real world actually gets the SPF that’s listed on the bottle,” says Dr. Curtis Asbury. “Nobody applies sunscreen thick enough to do so. Real world studies have been done which show that the average person wearing SPF 30 sunscreen only gets a fraction of that rating because they don’t apply enough. Because of this, everyone should wear the highest SPF they can reasonably use. If they use SPF 70 rated sunscreen, then maybe they will come close to actually getting SPF 30.”
It’s All About Ingredients
Not all our respondents stand by SPF numbers in the first place. Some are more focused on the active ingredients used. “Look for a zinc oxide and/or titanium dioxide sunscreen to get the best protection,” says Brenda Dintiman, M.D. “One that is waterproof and won’t burn your eyes when you’re running, biking, or swimming. It’s great for sensitive skin and won’t cause irritation. They’re all at least SPF 50 or above, and will prevent skin cancer and aging.”
One Number to Focus on: How Often You Reapply
Again, reapplication is key. You can’t cover yourself with a singular layer of SPF and expect it to shield you all day. “After hours of swimming or vigorous sweating, your SPF 100 is as good as SPF 15 if you aren’t regularly re-applying,” says Marcy Alvarez, DO. “I usually recommend sprays and aerosols for those with active lifestyles. Look for the words ‘80-minute water resistant’ and ‘invisible zinc.’”
Try Other UV-Blocking Measures
If you’re obsessing over effective coverage, then consider more than sunblock. “Something that’s often overlooked as an option for photoprotection is clothing,” says Audra Isaac Grossman, M.D. “There are many great brands available at various price points that offer lightweight UPF (ultraviolet protection factor) shirts, which eliminate some of the hassle of sunscreen reapplication.”
- Hanes UPF 50+ Long-sleeved Tees [$16; hanes.com]
- Coolibar UPF 50+ Long-sleeved Performance Tee [$55; coolibar.com]
She also recommends an oral supplement to help protect the skin: “Some daily antioxidants, like [fern-based] Heliocare, can also be beneficial in preventing UV damage but shouldn’t replace other sun protective measures.”