--- title: Sunscreens Work in the Sun, But UV Damage Continues Even in the Dark description: The latest studies reveal some surprising things about melanin, the compound responsible for tans, and the need for evening-after sunscreens canonical: https://time.com/3715036/sunscreens-after-dark/ author: Alice Park article:opinion: false article:content_tier: free article:published_time: 2015-02-19T19:03:40.000Z article:modified_time: 2026-05-11T05:05:32.780Z article:section: Health og:title: Why You Have to Worry About the Sun's UV Rays Even When It's Dark og:description: The latest studies reveal some surprising things about melanin, the compound responsible for tans, and the need for evening-after sunscreens og:url: https://time.com/3715036/sunscreens-after-dark/ og:site_name: TIME og:image: https://static.time.com/v3/assets/bltea6093859af6183b/bltfc793980e57d9f66/69877ffd524fc0bcd3dec8c1/829831801.jpg?branch=production&width=1200&quality=75&auto=webp&crop=16:9 og:image:width: 4992 og:image:height: 2808 og:image:alt: 82983180 og:type: article twitter:card: summary_large_image twitter:title: Why You Have to Worry About the Sun's UV Rays Even When It's Dark twitter:description: The latest studies reveal some surprising things about melanin, the compound responsible for tans, and the need for evening-after sunscreens twitter:image: https://static.time.com/v3/assets/bltea6093859af6183b/bltfc793980e57d9f66/69877ffd524fc0bcd3dec8c1/829831801.jpg?branch=production&width=1200&quality=75&auto=webp&crop=16:9 ---  # Here's Why You May Soon Be Using Sunscreen in the Dark > Sponsored content. 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Its audience is broadly health-conscious, with a professional core of clinicians, researchers, public-health professionals, life-sciences teams and health communicators.  by [Alice Park](https://time.com/author/alice-park/)  ## Alice Park Senior Correspondent Feb 19, 2015 7:03 PM UTC   by [Alice Park](https://time.com/author/alice-park/)  ## Alice Park Senior Correspondent Feb 19, 2015 7:03 PM UTC The [guidelines for sun exposure](http://www.skincancer.org/prevention/sun-protection/prevention-guidelines) are pretty familiar by now—cover up exposed skin, steer clear of the peak UV streaming hours of 10 am to 2pm, and always, always wear [sunscreen](http://time.com/109249/yes-you-need-to-wear-sunscreen-everywhere-heres-how/). Now, in a series of [experiments described in the journal _Science_](http://www.sciencemag.org/lookup/doi/10.1126/science.1256022), researchers say that may not be enough to shield against skin cancer. Working with human cells in a lab dish, as well as with mouse models, they found that melanin—which is produced in response to UV exposure to protect sensitive skin from being damaged—may have a dark side to its skin-protecting role. And, even more concerning, the harm triggered by the sun’s rays may linger long after the sun sets. **MORE:** [You Asked: Is Sunscreen Safe—And Do I Really Need It Daily?](http://time.com/3056125/you-asked-is-sunscreen-safe-and-do-i-really-need-it-daily/) Douglas Brash, professor of therapeutic radiology and dermatology at Yale University School of Medicine, and his colleagues say that activating melanin has lasting effects—some positive, but mostly negative—on the body’s chemistry for up to three hours after sun exposure. That could mean that the risk of skin cancer from agents generated by UV damage continues even in the dark, they add. ### You Asked: Your Top 10 Health Questions Answered  You Asked: Are Cleanses Healthy? Potions that claim to clear your body of toxins might sound alluring, but do they deliver? Illustration by Peter Oumanski for TIME  You Asked: Is Eating Dessert Really That Bad For Me? Bad news for sweet-eaters—except if you end your meals with this kind of treat. Illustration by Peter Oumanski for TIME  You Asked: What’s the Best Way to Whiten My Teeth? Yes, teeth whitening actually works—but here's why you have to dish out major bucks to see results. Illustration by Peter Oumanski for TIME  You Asked: Is Meditation Really Worth It? From easing stress to lowering heart disease risk, focusing your mind can do some amazing things for your body. Illustration by Peter Oumanski for TIME  You Asked: What’s the Healthiest Sweetener? Take a taste of the unsettled science of sweeteners. Illustration by Peter Oumanski for TIME  You Asked: Should I Go Paleo? The pros and cons of eating like a caveman. Illustration by Peter Oumanski for TIME  You Asked: Is Cracking Your Knuckles Bad? Here's what really happens to your joints when you snap, crackle and pop. Illustration by Peter Oumanski for TIME  You Asked: Is Running on a Treadmill as Good as Running Outside? You'll fool your body into thinking it's outside with this one small treadmill tweak. Illustration by Peter Oumanski for TIME  You Asked: Does Laughing Have Real Health Benefits? Here's proof that everybody could use a belly laugh. Illustration by Peter Oumanski for TIME  You Asked: What Is My Poo Telling Me? If you listen hard enough, you'll hear all kinds of health stories from #2. Illustration by Peter Oumanski for TIME Melanin is supposed to be the body’s natural sunblock. It’s released in response to UV light and protects delicate skin from burning, as well as the DNA deeper in skin cells from being scrambled so they don’t cause cancer. But when the scientists exposed mouse cells to UV light, they found that the melanin-containing cells produced mutations, and continued to do so for three hours after the light was removed. Similar cells from albino mice, which are missing melanin, didn’t show the same effect. Human melanin-containing cells also generated these damaging changes long after exposure. **MORE:** [We’re One Step Closer to Better Sunscreen](http://time.com/2992200/were-one-step-closer-to-better-sunscreen/) The vast span of time during which damage could occur after exposure surprised the researchers. “To have the \[changes\] made after exposure is like having a process that should have taken a second during the time of the dinosaurs just finish up today,” says Brash. “That’s how bizarre this is.” Once activated, he says, some of the melanin is highly energized, and in that state, starts to degrade. “When you create high-energy molecules, the energy has to go somewhere,” says Brash. In some cases, it transfers to the DNA where it continues to monkey with normal DNA codes for hours. **MORE:** [Obama Signs Law for Better Sunscreen](http://time.com/3611787/better-sunscreen-law/) The good news is that this process can be interrupted, as long as the excess energy has an outlet. “If we can divert some of that energy to another molecule and change it into heat, it doesn’t cause problems,” says Brash. In the study, he experimented with some agents including vitamin E, which eliminated the harmful high-energy agents, and kojic acid, which reduced them by 85%. But it’s not clear yet how these agents should be used or for how long after sun exposure. The findings do make a strong case, however, that applying sunscreen after being out in the sun might become just as important as slathering them on while outside. In the meantime, “continue doing what you’re doing and use sunscreen,” says Brash. “Sunscreens do block UV wavelengths, and will prevent some of these processes from starting. And the lower dose of exposure you have, the better off you are. We just might have to start considering continuing that protection a little longer than we thought.” ```json [{"@context":"https://schema.org","@type":"NewsArticle","@id":"https://time.com/3715036/sunscreens-after-dark/","mainEntityOfPage":{"@type":"WebPage","@id":"https://time.com/3715036/sunscreens-after-dark/"},"headline":"Here's Why You May Soon Be Using Sunscreen in the Dark","datePublished":"2015-02-19T19:03:40.000Z","dateModified":"2026-05-11T05:05:32.780Z","description":"The latest studies reveal some surprising things about melanin, the compound responsible for tans, and the need for sunscreen after sun exposure","url":"https://time.com/3715036/sunscreens-after-dark/","keywords":["medicine","skin cancer"],"thumbnailUrl":"https://static.time.com/v3/assets/bltea6093859af6183b/bltfc793980e57d9f66/69877ffd524fc0bcd3dec8c1/829831801.jpg?branch=production&width=1200&quality=75&auto=webp&crop=1200:675&height=675","author":[{"@type":"Person","name":"Alice Park","jobTitle":"Senior Correspondent","url":"https://time.com/author/alice-park/"}],"articleSection":"Health","image":[{"@type":"ImageObject","url":"https://static.time.com/v3/assets/bltea6093859af6183b/bltfc793980e57d9f66/69877ffd524fc0bcd3dec8c1/829831801.jpg?branch=production&width=1200&quality=75&auto=webp&crop=1200:675&height=675","width":1200,"height":675,"headline":"82983180","caption":"","creditText":"","representativeOfPage":true}],"publisher":{"@type":"Organization","name":"Time","url":"https://time.com/","logo":{"@type":"ImageObject","url":"https://time.com/images/logo.png","width":528,"height":156},"foundingDate":"March 3, 1923","sameAs":["https://www.facebook.com/time","https://www.instagram.com/time/?hl=en","https://twitter.com/time","https://www.pinterest.com/timemagazine"]}},{"@context":"https://schema.org","@type":"BreadcrumbList","itemListElement":[{"@type":"ListItem","position":1,"item":{"@id":"/section/health/","name":"Health"}},{"@type":"ListItem","position":2,"item":{"@id":"/tag/medicine/","name":"medicine"}},{"@type":"ListItem","position":3,"item":{"@id":"https://time.com/3715036/sunscreens-after-dark/","name":"Here's Why You May Soon Be Using Sunscreen in the Dark"}}]}] ```