Sun Savvy: 5 Surprising Facts About SPF

by Natalie Higdon, Birchbox

How to get the most out of your sunscreen. Read on for our tips and tricks.
We've all heard the basic facts about sunscreen: apply 15-30 minutes before sun exposure; wear daily to prevent premature aging; reapply after swimming. But there are some gray areas. Can you use leftover sunscreen from last year? What about tinted moisturizer with SPF-is that enough? We went to the experts to get answers-and you're going to be surprised by what we learned.

1. EXPIRED SUNSCREEN CAN DO MORE HARM THAN GOOD
"Using an expired sunscreen can lead to reduced protection from UV rays due to diminished SPF," says Holly Thaggard, Founder and CEO of Supergoop!. Plus, Thaggard says, expired formulas can also contain bacteria and fungus growth (yuck!). Elizabeth Hale, M.D., board certified dermatologist and a Clinical Associate Professor of Dermatology at New York University Langone Medical Center, adds, "Sunscreens degrade in hot temperatures, so those left in the glove compartment, for example, might lose their effectiveness well before the expiration date." No expiration date? Toss after one year.

Related: Skincare Matchmaker: Sun Protection

2. REAPPLY EVERY TWO HOURS - NO EXCEPTIONS
One coat isn't enough to protect your skin all day, whether you're swimming or not. "Even the best sunscreens need to be reapplied every two hours," Dr. Hale says. Thaggard's memory trick? "If you'll be out in the sun for long periods, set a reminder on your phone to reapply."

3. SUNSCREEN IS A MUST EVEN WHEN YOU'RE INDOORS
Notice more freckling or discoloration on the left side of your face? That's likely a result of UV rays penetrating through your driver's side window. UV rays aren't blocked by clouds or glass, which means you'll need plenty of SPF even if you spend your days at a desk.

Related: Sunscreen: Cheat Sheet

4. CHEMICAL AND MINERAL SUNSCREENS ARE BOTH EFFECTIVE - BUT WORK DIFFERENTLY
Chemical sunscreens absorb the sun's UV rays; mineral sunscreens block those rays. Both are FDA-approved, and Dr. Hale agrees that chemical sunscreens are safe and effective. However, since many consumers now prefer natural formulations, mineral sunscreen is gaining popularity.

5. MAKEUP WITH SPF ISN'T ENOUGH TO PROTECT YOUR SKIN
To get the benefits of the SPF listed on the bottle, you need to apply one teaspoon for the exposed areas of your face and neck-way more foundation or powder than you'd ever need. Dr. Hale says, "I tell patients those are nice as supplements, but you should put on a good base of sunscreen every day."

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