--- title: UVA, UVB and Skin Cancer: Do You Know What Sunscreen SPF Means? description: How much do you know about sunscreen labels? Here's what to know about UVA, UVB, SPF and sun protection. canonical: https://time.com/3924609/sunscreen-spf-uva-uvb/ author: Mandy Oaklander article:opinion: false article:content_tier: free article:published_time: 2015-06-17T17:37:23.000Z article:modified_time: 2026-05-11T05:02:59.841Z article:section: Health og:title: This Is the Only Sunscreen Article You Need to Read og:description: How much do you know about sunscreen labels? Here's what to know about UVA, UVB, SPF and sun protection. og:url: https://time.com/3924609/sunscreen-spf-uva-uvb/ og:site_name: TIME og:image: https://static.time.com/v3/assets/bltea6093859af6183b/blt4526db8fe3a3e4a2/698854e355a8591ea9a8c899/sunscreen-suntan-lotion.jpg?branch=production&width=1200&quality=75&auto=webp&crop=16:9 og:image:width: 4134 og:image:height: 2325 og:image:alt: sunscreen-suntan-lotion og:type: article twitter:card: summary_large_image twitter:title: This Is the Only Sunscreen Article You Need to Read twitter:description: How much do you know about sunscreen labels? Here's what to know about UVA, UVB, SPF and sun protection. twitter:image: https://static.time.com/v3/assets/bltea6093859af6183b/blt4526db8fe3a3e4a2/698854e355a8591ea9a8c899/sunscreen-suntan-lotion.jpg?branch=production&width=1200&quality=75&auto=webp&crop=16:9 ---  # This Is the Only Sunscreen Article You Need to Read > Sponsored content. Supplied in partnership with TIME. 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Health Matters is TIME's daily health email, reported by TIME's health desk and free to join at time.com/newsletters. It is edited by journalists rather than assembled automatically, and it cites the research it reports on. #### Is Health Matters free? Yes. Health Matters is a free daily newsletter from TIME, available at time.com/newsletters. #### Who reads TIME's Health Matters newsletter? Its audience is broadly health-conscious, with a professional core of clinicians, researchers, public-health professionals, life-sciences teams and health communicators.  by [Mandy Oaklander](https://time.com/author/mandy-oaklander/)  ## Mandy Oaklander Oaklander is a senior editor at TIME. Jun 17, 2015 5:37 PM UTC  Getty Images  by [Mandy Oaklander](https://time.com/author/mandy-oaklander/)  ## Mandy Oaklander Oaklander is a senior editor at TIME. Jun 17, 2015 5:37 PM UTC How proficient are you in sunscreen-ese? According to a new [survey](http://archderm.jamanetwork.com/article.aspx?articleid=2319715) in _JAMA Dermatology_, most people don’t understand much of what’s written on a lotion label. Researchers at Northwestern University Feinberg School of Medicine wanted to test people’s knowledge of sunscreen, so they surveyed 114 people who came to the dermatology clinic during the summer of 2014\. Even though 93% of them had purchased a bottle in the last year, most people showed important gaps in their sunscreen smarts. **1\. UVB rays** “People think that SPF equals everything,” says Dr. Roopal Kundu, one of the study’s authors and a dermatologist at Northwestern University Feinberg School of Medicine. And it does count for a lot: the sun protection factor measures a sunscreen’s ability to filter UVB rays, which are related to [sunburn and skin cancer](http://time.com/3907272/skin-cancer-rates-melanoma/). But SPF _only_ measures UVB rays; it doesn’t tell you anything about protection from UVA rays, Kundu says. **Read More**: [Top Sunscreens Are Put To The Test](http://time.com/3917706/top-sunscreens-are-put-to-the-test/) **2\. UVA rays** The most misunderstood part of sunscreen is UVA, Kundu says. “UVA is around every day; it can penetrate through window glass,” she says. Like UVB, it’s also related to an increased risk of skin cancer, but unlike UVB, it’s not filtered by the ozone at all, Kundu says. UVA doesn’t cause sunburn, but “it really leads to darkening and aging, because it penetrates deeper into the skin and has more influence in the collagen.” There’s only one way to tell whether your sunscreen offers UVA coverage: the words “broad spectrum.” Only 34% of people in the study named “broad spectrum” labeling as an influence in their choice to buy a sunscreen, but they’re the two most crucial words to look for on a sunscreen label, Kundu says, because there’s no other metric on the bottle for UV-A coverage. Without the words “broad spectrum” your sunscreen likely doesn’t offer coverage from UVA, Kundu says. Most active ingredients in sunscreen shield against UVB, but far fewer have UVA coverage, and only a handful offer both. Personally, Kundu uses an SPF 30 sunscreen with the active ingredient zinc oxide, a natural sunscreen ingredient that physically—instead of chemically—blocks rays. Zinc oxide protects against both UVA and UVB rays. **Read More:** [80% Of Sunscreens Don’t Really Work Or Have ‘Worrisome’ Ingredients: Report](http://time.com/3883293/sunscreen-spf/) ### See New York's Beaches From Above  Coney Island, Brooklyn. Tobias Hutzler  Rockaway, Queens. Tobias Hutzler  The People's Beach at Jacob Riis Park, Queens. Tobias Hutzler  Brighton Beach, Brooklyn. Tobias Hutzler  Coney Island, Brooklyn. Tobias Hutzler  Brighton Beach, Brooklyn. Tobias Hutzler  Coney Island, Brooklyn. Tobias Hutzler  Rockaway Beach, Queens. Tobias Hutzler  Brighton Beach, Brooklyn. Tobias Hutzler  Coney Island, Brooklyn. Tobias Hutzler  New Boardwalk, Coney Island, Brooklyn. Tobias Hutzler  Coney Island, Brooklyn. Tobias Hutzler  MacCarren Pool Williamsburg, Brooklyn. Tobias Hutzler  Lasker Pool, Central Park, Manhattan. Tobias Hutzler  Astoria Park Pool, Queens. Tobias Hutzler  Astoria Park Pool, Queens. Tobias Hutzler  Orchard Beach, Bronx. Tobias Hutzler  South Beach, Staten Island. Tobias Hutzler  Orchard Beach, Bronx. Tobias Hutzler  South Beach, Staten Island. Tobias Hutzler  Coney Island, Brooklyn. Tobias Hutzler  Central Park, Manhattan. Tobias Hutzler **3\. SPF numbers** So why does a dermatologist only use an SPF of 30? People in the study rated a high SPF number as the number-one reason they bought one sunscreen over another, but only 43% of people in the study knew what _SPF_ actually meant. Here’s the real definition: an SPF of 30 means that technically, you could be out in the sun 30 times longer before you get sunburned than you would be able to if you went out without sunscreen, as long as you keep reapplying it appropriately, Kundu says. And an SPF of 15 is _not_ half as effective as an SPF 30, contrary to what 39% of the people in the study thought. According to Kundu, SPF 15 filters about 93% of UV-B rays; SPF 30 filters about 97% of UV-B rays; and SPF 50 filters about 98% of UV-B rays. The difference between SPF 30 and SPF 50 is only a 1% filtering improvement, she says, and since SPF 30 is readily available at many different price points, that’s the one many dermatologists recommend. **4\. How much you need** For a sunscreen to work as advertised, you have to use a shotglass worth for unexposed areas, Kundu says. (About half of people in the study got this wrong.) **Bottom line**: Typical adults should buy a water-resistant, broad-spectrum SPF 30 sunscreen, reapply every two hours and use the right amount, Kundu says. “If we can help reduce or spot skin cancer sooner, or be more aware of it, these are the mechanisms by which we can do it.” ```json [{"@context":"https://schema.org","@type":"NewsArticle","@id":"https://time.com/3924609/sunscreen-spf-uva-uvb/","mainEntityOfPage":{"@type":"WebPage","@id":"https://time.com/3924609/sunscreen-spf-uva-uvb/"},"headline":"This Is the Only Sunscreen Article You Need to Read","datePublished":"2015-06-17T17:37:23.000Z","dateModified":"2026-05-11T05:02:59.841Z","description":"Only 43% of people know the definition of SPF","url":"https://time.com/3924609/sunscreen-spf-uva-uvb/","keywords":["Public Health","UVA","sunscreen","Know Right Now"],"thumbnailUrl":"https://static.time.com/v3/assets/bltea6093859af6183b/blt4526db8fe3a3e4a2/698854e355a8591ea9a8c899/sunscreen-suntan-lotion.jpg?branch=production&width=1200&quality=75&auto=webp&crop=1200:675&height=675","author":[{"@type":"Person","name":"Mandy Oaklander","jobTitle":"Oaklander is a senior editor at TIME.","url":"https://time.com/author/mandy-oaklander/"}],"articleSection":"Health","image":[{"@type":"ImageObject","url":"https://static.time.com/v3/assets/bltea6093859af6183b/blt4526db8fe3a3e4a2/698854e355a8591ea9a8c899/sunscreen-suntan-lotion.jpg?branch=production&width=1200&quality=75&auto=webp&crop=1200:675&height=675","width":1200,"height":675,"headline":"sunscreen-suntan-lotion","caption":"sunscreen-suntan-lotion","creditText":"Getty Images","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/public-health/","name":"Public Health"}},{"@type":"ListItem","position":3,"item":{"@id":"https://time.com/3924609/sunscreen-spf-uva-uvb/","name":"This Is the Only Sunscreen Article You Need to Read"}}]}] ```