Everything Your Dermatologist Wishes You Knew About Sunscreen

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In her imaginary college commencement speech, published in the Chicago Tribune, Mary Schmich writes: “If I could offer you only one tip for the future, sunscreen would be it.” Protecting your skin from the sun is a health and beauty non-negotiable, there’s no doubt about that, but are you using the right formula in the most effective way? We asked Dr. Joyce Park, an NYU dermatology resident, to address the most common queries and myths about sunscreen.

Culture Trip: Are all sunscreens equally effective?

Dr. Joyce Park: There are two sunscreen ingredients on the market, physical blockers like zinc oxide and titanium dioxide that block both UVA and UVB radiation by reflecting the sun’s radiation, and chemical blockers like oxybenzone that block radiation by absorbing it and converting it into heat. The one thing about chemical blockers is that they only block UVB, so they need to be used with a UVA blocking agent. Because of this some prefer physical blockers.

CT: How do SPFs work and which factor should I use?

JP: SPF is a measurement of how much a sunscreen protects your skin from UVB radiation from the sun. It measures how much longer it takes your skin to redden with SPF on verses without SPF sunscreen on. For example, if it takes 20 minutes in the sun for your skin to redden, use of an SPF 30 would protect your skin from reddening 30 times that, 10 hours. SPF 15 blocks about 93 percent of the sun’s rays, SPF 30 blocks about 97 percent, and SPF 50 blocks about 98 percent. Dermatologists recommend using SPF 30 and above to be safe, since most people are not applying sunscreen as thickly as they should to receive its full benefits.

CT: Is there a good “clean” sunscreen?

JP: There is a lot of inaccurate information out there regarding “clean” versus “unsafe” ingredients in sunscreens. A thorough dig into the scientific literature on key ingredients in sunscreen makes the many claims by groups such as the Environmental Working Group Sunscreen (EWG) seem unconvincing. The EWG points out oxybenzone and retinyl palmitate as harmful ingredients but if you look at the actual scientific studies, there is no evidence that topical application through sunscreen cause humans any sort of harm at all. If you have sensitive allergy-prone skin, however, that is another issue. You may want to avoid products containing oxybenzone, since that has been known to cause allergic reactions. If you’re prone to pimples, you may want to look for non-comedogenic sunscreens as well.

CT: Is a factor 30 the same strength across the board, or are some brands more reliable than others?

JP: Not all sunscreens actually meet the SPF they claim on the packaging, according to Consumer Reports. Be sure to buy sunscreens from trusted brands in order to get the actual sun protection you pay for. If you have questions about which brands are trustworthy, speak to your local dermatologist.

CT: Is there a recommended technique for applying sunscreen?

JP: The important things to know are when to apply sunscreen, how much to apply, and when to reapply. You should apply sunscreen 15 minutes before you go outside, and in order to get the stated SPF on the bottle apply about a shot glass worth of sunscreen to all sun exposed areas. Remember to reapply every two hours, and to seek shade during peak sun exposure — 10 am to 4 pm.

CT: Does the expiry date on sunscreen bottles really mean anything?

JP: I would abide by the expiration date because the sunscreen ingredients may not be effective at its original strength past its shelf life.

CT: What else should everybody know about protecting their skin?

JP: As a dermatologist, this is one of the topics I try to talk to all my patients about. I advise using sunscreen SPF 30 everyday, rain or shine, because UVA and UVB radiation increase your risk of skin cancer and cause photoaging. Whenever any of my patients tell me they tan, I explain to them that the extra sun exposure will age their skin, causing wrinkles, brown spots, and sagging leathery skin. Just check out this photo of sun-induced aging on just half of this truck driver’s exposed face if you don’t believe me. UVA causes photoaging and skin cancer, and UVB exposure causes DNA damage that results in skin cancers. Sunscreen is your invisible shield that will help block all of these rays!

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