In theory, sunscreen should be an uncomplicated affair: If you slather it on every day, you’re protected, and if not, you’re not. Simple, right?
Yet somehow, there are so many factors that make things rather confusing. For example, what is the difference between chemical and physical formulas? SPF 100 is way better than SPF 30, right? Is this bottle I bought two years ago still any good? Hold up—how does this stuff actually work, anyway?
You’re not alone—these are things we’ve pondered ourselves. So to clear things up, we’re tackling some of the biggest FAQs about SPF, as well as facts you’ve probably never even considered. Get the answers to your burning questions (see what we did there?) below.
Given that most cosmetics tend to expire within a year or two, you might be surprised to learn that SPF is formulated to be effective for up to three years. Better yet, most bottles are stamped with an expiration date, so if you’re unsure or don’t remember when you bought it, try checking the label or the bottom. (And if it smells funny or changes color, it’s best just to toss it.)
Along with the ears and scalp, nails (fingers and toes alike) are some of the most overlooked places when people lather up—which leaves the skin underneath all the more vulnerable to skin cancer. Rule of thumb: Just put it everywhere.
Earlier this year, Consumer Reports revealed that nearly half the formulas tested in its annual sunscreen report didn’t live up to the SPF number listed on the bottle. To be sure you’re getting ample protection, consider picking one of the products Consumer Reports did approve—like La Roche-Posay’s Anthelios ($30), which was the only formula to receive a perfect score.
You’re just fine sticking with SPF 30. “There is very little difference [between] an SPF 30, 50, or 100 when it comes to blocking UV rays,” dermatologist Dr. Elizabeth Tanzi told us. SPF 30 already blocks 97% of those rays, and in reality, upgrading to 50, 75, or 100 makes very little difference—we’re talking 1% or 2%. (In fact, the FDA has proposed capping the number displayed at SPF 50.)
The FDA is cracking down on sunscreen labeling this year, and one of the provisions includes prohibiting the use of words like waterproof and sweatproof. Even if an SPF is water-resistant, says the organization, it still wears off as the day goes on—and claiming that it’s waterproof might deter people from reapplying. (You should be constantly reapplying no matter what formula you’re using.) In addition, bottles labeled “water-resistant” will need to also inform the user how often to reapply when swimming or sweating—the options are every 40 or 80 minutes.
Fried, damaged hair is not a cute look, and that’s not even to mention that if you color your hair, you’re basically throwing money out every time you step outside without protection. Use an SPF hair mist like Shiseido’s Ultimate Sun Protection Spray ($36), which can conveniently be used on your face and body, too. Better yet, pair it with a hat.
Both formulations have pros and cons, and work slightly differently. The SparkNotes version: Physical sunscreen contains mineral ingredients (like zinc) that sit on top of your skin to refract the sun’s rays. Chemical formulas contain organic compounds that are absorbed by the skin and react with UV rays, releasing them as just heat. Both are very effective, so it really comes down to personal preference. But esthetician Renée Rouleau makes the case for using both, so you can get protection both inside and out.
For a long time, any sunscreen manufacturer could stamp “broad spectrum” on the bottle even if the formula only technically protected from UVB rays—which is exactly the case for many sunscreen products sold in the US. The FDA is now cracking down on this, but it’s worth noting that if your go-to formula only protects from UVB rays, you’re not being as safe as you could. While UVB rays are the chief culprit behind sunburns, UVA rays are associated with skin cancer as well, not to mention skin-damaging (and aging) free radicals. Opt for a formula that either offers certified broad spectrum protection or uses zinc oxide as its main ingredient, which is the most effective UVA-filtering ingredient currently approved by the FDA.
On that note, many dermatologists recommend selecting European formulas rather than American, since they tend to contain better UVA filters and thus offer more protection against free radicals—making for far more extensive protection. (Remember, it’s not just about preventing a burn.) Again, we’re huge fans of La Roche-Posay’s very extensive range.
Want to step up your sun protection even further? From an SPF-depositing face wash to a UV-monitoring sticker, these are the most innovative products on the market right now.