Everything You Didn't Know About Sunscreen

But you're about to learn! (And you'll be glad you did.)

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This is the first installment of The Sweet Guide to Sun Care 2016, which will focus on the tips, information, and commentary that'll help you better understand sun protection—so you can safely frolic outdoors all summer long.

Even though SPF is often a daily staple in our skin-care routines, there are a couple of things about applying sunscreen that almost universally stump people. For example: Do you know the amount of sunscreen you should apply to your face, neck, arms, and legs on days spent in full sun? You can take a guess, of course, but there's a trick that will help you never forget the answer.

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UV Physical Broad Spectrum SPF 41 Sunscreen by EltaMD, $30, dermstore.com.
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Here, Dr. Michael H. Swann of Springfield, Missouri's Swann Dermatology and Esthetics—an expert on all things skin—shares some extremely important details regarding our daily dose of SPF.

(You'll want to save them!)

The Real Meaning Behind SPF Numbers

SPF numbers seem to be self-explanatory—the higher the number, the more protection, right? Well, yes, but some days you don't really need an SPF above 30. Dr. Swann explains the science behind the numbers, using SPF 50 as an example.

"The SPF rating means that the same redness you would get in one hour without sunscreen would take you 50 hours to get with sunscreen," he says. "You don't need 50 hours worth of protection for a one-hour kind of thing, or a day mostly spent inside." Unless you burn easily, or will be outside for an extended period of time, lower SPFs are safe. The SPF number makes more of a difference when you don't apply the correct amount—which brings us to our next tip.

Umbra Sheer Physical Defense SPF 30 by Drunk Elephant, $38, sephora.com.
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You're Almost Definitely Not Applying the Right Amount of Sunscreen

"People use a third to a fourth of the amount of sunscreen they're supposed to on their faces and necks when applying it," Dr. Swann says.

"A tablespoon is good for your face and neck, and one ounce—or the volume of a shot glass—is best for your exposed arms and legs," Dr. Swann says. If you're in a swimsuit, another ounce of sunscreen will take care of other exposed areas, like your stomach and shoulders. 

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If you tend to put on less sunscreen, use a higher SPF, at least. "If someone uses [a small amount of] an SPF 15, there's no way they are getting the full SPF 15—they're getting more like an SPF 3 or 4." Always keep in mind that you can't really go overboard with your sunscreen.

Know the Difference Between Chemical and Physical Formulas

Sunscreens can degrade over the course of a day. That's why it's important to reapply if you're outdoors and active. There are two types of formulas you should be aware of: chemical SPF, which combines manufactured compounds to promote a chemical reaction that protects the skin against rays. Then there's physical SPF, which features minerals to reflect sunlight. 

Sheer Physical Broad Spectrum Sunscreen SPF 50 Plus by Replenix, $38, dermstore.com.

If you use a chemical SPF instead of a physical kind, you're receiving less protection. Here's why.

"Physical and chemical sunscreens work really differently," Dr. Swann says. "Chemical sunscreens are 90 percent of what's available in stores and they mainly protect you from UVB, which combats redness—the SPF is the UVB rating." He continues: "They don't do a very good job at protecting you from UVA rays, which are primarily responsible for most of what we care about with aging, spots on your face, and melanoma." 

Sheer Fluid Sun Shield, $52, lancerskincare.com.

Physical formulas, however, do it all. "Physical sunscreens protect you really well from UVA and UVB, because they have mineral bases, such as zinc and titanium," he says. "The minerals function like little mirrors on your skin. That's why when a physical sunscreen is applied to skin, it gives a little bit of sheen or glow, because it's reflecting off the light."

Chemical sunscreens aren't bad for everyday wear, but make sure to have a physical formula for when you're outside more often (like, say, when you're splashing around in the ocean under the summer sun!). 

Skin Soothing Mineral Sunscreen with Olive Polyphenols SPF 40, $28, supergoop.com.
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There Should Be an Order to Your Morning Routine

The timing of your sunscreen application is also critical. "A serum or anything that's really more of a medication should go on first," Dr. Swann says, adding, "put things on by heaviness—light things go on first (like the serums or gels), then onto moisturizer (if extra is needed), then your sunscreen on the outside."

Dr. Swann also notes that mineral sunscreens are great to put on right before makeup application, as they can act as a primer. One product, multiple uses!  

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