Your sunscreen is chockfull of active ingredients and there's an expiration date for a reason. Shari Marchbein, a board-certified New York dermatologist, says it's like food—the ingredients can spoil or oxidize and become less effective. And like food, leaving it in a warm place, like a car or by the pool, will ensure it spoils faster due to the heat. Another problem? Bacteria can grow in a dormant bottle that's been sitting around for a year. Your best bet? Start fresh with a new bottle every summer.
Not All SunscreenIs Created Equal
There are essentially two types of sunscreen: chemical and physical. Chemical sunscreens contain ingredients such as oxybenzone, avobenzone and homosalate, which absorb UV rays, convert them into heat, which is then released from the body. Physical, or mineral, sunscreens utilize minerals such as titanium dioxide and zinc oxide to create a physical barrier between your skin and the sun's rays. They're regarded as more natural, but they often leave a white cast on your skin (not ideal for people of color). As for chemical sunscreens, a recent FDA study showed that the active ingredients were absorbed into the bloodstream, but there is no current data to suggest that this is dangerous. Remember, not all chemicals are bad or dangerous.
You Need aDecent Amount
You might've heard that you need an entire shot glass's worth of sunblock to cover your face and body. Marchbein says that's exactly right. The majority of cream sunscreens have about three ounces in a bottle. Sprays are more like four to eight ounces—so you could be applying up to a quarter of the bottle every application.
Waterproof Isn’tExactly True
You have to reapply if you're out in the sun for the day. Most dermatologists recommend every two to four hours. Especially for chemical blockers that slowly breakdown as they're exposed to UV light. Even for those bottles that are labeled as waterproof or sweat-resistant—sure, they'll stick to your body better than standard sunscreen, but they still require you to reapply. And be sure to allow sunscreen to settle on the skin for at least 10 to 15 minutes before going into the water.
SPF Is Important
(But Not Everything)
Dr. Craig Austin, a board-certified dermatologist and dermatopathologist, breaks down SPF (Sun Protection Factor) like this: Let's say you normally turn red after ten minutes in the sun. If a sunscreen is rated SPF 15, it would take 15 times your normal exposure time for the skin to turn red. Which means it would take about 150 minutes before you'd start to burn. The higher the SPF, the longer you can go before reapplying, but it doesn't provide significantly more protection at any particular moment, he says. Dermatologists recommend using an SPF of 30 or higher on summer days when the sun's rays are most intense. But it's also worth noting that higher SPF formulas often come with more concentrated chemicals, which can be irritating to sensitive skin.
You Can Still TanWith Sunscreen
Your sunscreen helps protect against damage from ultra violet (UVA and UVB) rays, but it doesn't shield your body entirely. Your skin will still develop color. That's your body's natural protective response to UV exposure. And you're still able to get your daily dose of Vitamin D. Especially because you only need 10 to 15 minutes of sun each day before your body reaches maximum production of vitamin D and then it stops.