No, last year’s bot­tle of sun­screen won’t nec­es­sar­ily pro­tect you from get­ting burned.

The Washington Post Sunday - - OUTLOOK - By Boer Deng Boer Deng writes for Na­ture. Twit­ter: @boer­deng

Sum­mer’s smell — sun, sea, san­dals, shore — lives in the vague sweet­ness of sun­screen. Sun­block is one of the sea­son’s totems, along with pink-jack­eted pa­per­backs and bot­tles of lime-fa­vored beer. But for all its ubiq­uity, the elixir is of­ten mis­used. Here are five myths, dis­pelled to help you pro­tect your­self bet­ter.

You need sun­screen only on sunny days.

Plenty of peo­ple have had the un­pleas­ant ex­pe­ri­ence of go­ing out on a cool, over­cast day — too rare dur­ing Wash­ing­ton sum­mers — only to re­turn with a nasty sun­burn. Yet one of the most-cited rea­sons for for­go­ing sun­screen is cloud cover. When clouds are shroud­ing the sun, it’s easy to think that they’re pro­tect­ing you from its rays. But un­like light or warmth, the sun’s skin-dam­ag­ing ul­tra­vi­o­let ra­di­a­tion can’t be per­ceived di­rectly. Although clouds block some UV ra­di­a­tion, 80 per­cent still reaches the Earth’s sur­face. Clouds can also have the ef­fect of re­flect­ing UV rays, en­hanc­ing their reach.

The SPF is what mat­ters.

Ad­vice about sun­screen in­vari­ably be­gins with the rec­om­men­da­tion to use some­thing with an SPF value of 15 or greater, giv­ing the im­pres­sion that those three familiar let­ters are all you need to de­cide which sun­screen to buy. But SPF (“sun pro­tec­tion fac­tor”) is more akin to me­ter-mark­ers at the lo­cal pool — a gauge for what might suit a par­tic­u­lar swim­mer. It’s an ap­prox­i­ma­tion of how much time you can spend in the sun with­out burning. An SPF 15 sun­screen, for ex­am­ple, will al­low you to stay ex­posed 15 times longer with­out burning than if your skin was un­pro­tected, while an SPF 30 prod­uct is said to ex­tend this 30 times. Pro­tec­tive­ness against UV rays does not scale in pro­por­tion to the SPF value, how­ever: SPF 15 lo­tions block 93 per­cent of UV rays; SPF 30, about 97 per­cent.

Nor is SPF ef­fi­cacy ex­act. Testers ar­rive at the fig­ure by ap­ply­ing two mil­ligrams of sun­screen to a square cen­time­ter of skin. Users reg­u­larly ap­ply less — only a quar­ter or half that amount, by one es­ti­mate. More­over, not all sun­screen for­mu­la­tions are the same: Seven­teen sun-fil­ter­ing mol­e­cules are ap­proved by the Food and Drug Ad­min­is­tra­tion for block­ing var­i­ous lengths of UV ra­di­a­tion, which ranges from 200 to 400 nanome­ters on the elec­tro­mag­netic spec­trum. Other in­gre­di­ents con­fer wa­ter re­sis­tance or chem­i­cal sta­bil­ity, which changes how long UV pro­tec­tion lasts.

Some­times, an in­flated SPF value of­fers mis­lead­ing as­sur­ance with lit­tle mean­ing (surely the de­but of an SPF 200+ lo­tion would bring “a world with­out poverty,” quipped a New Yorker hu­mor col­umn). In fact, the false safety im­plied by ever-higher SPF num­bers in­spired reg­u­la­tors in Europe, Ja­pan and Australia to cap SPF val­ues. Sun­screens sold in those mar­kets do not ex­ceed 50.

Darker-skinned peo­ple have less need for sun­screen.

It’s true that some of us are more sus­cep­ti­ble to sun­burn than oth­ers. In part, this is re­lated to the pres­ence of melanin, a pig­ment in skin that ab­sorbs wave­lengths of UV ra­di­a­tion. But that nat­u­ral shield is not so strong that sun­screen can be jet­ti­soned: Melanin is thought to of­fer an SPF value of 1.5 to 2.0 and is less ef­fec­tive at block­ing the most dam­ag­ing UV rays, known as UVA ra­di­a­tion, which pen­e­trate deeper into skin.

The mis­taken no­tion that dark skin is nat­u­rally more pro­tected prop­a­gates in in­sid­i­ous ways. For ex­am­ple, a 2006 study found that sun­block ads are much more preva­lent in mag­a­zines with pre­dom­i­nantly white read­er­ships, com­pared with those aimed at black au­di­ences. Myths about sun pro­tec­tion among African Amer­i­cans can have lethal con­se­quences: Though the in­ci­dence of skin can­cer among blacks is low com­pared with other groups, their sur­vival out­comes are poorer— a 73 per­cent five-year sur­vival rate com­pared with a rate of 91 per­cent for whites. This is partly be­cause of dif­fer­ences in ac­cess to med­i­cal care and partly be­cause of the types of skin can­cers that dis­pro­por­tion­ately strike dark-skinned peo­ple, in­clud­ing the ag­gres­sive acral lentig­i­nous melanoma. A lack of aware­ness of skin can­cer risks among African Amer­i­cans is thought to con­trib­ute to black pa­tients not seek­ing treat­ment im­me­di­ately for sus­pi­cious skin le­sions; as a re­sult, many African Amer­i­cans present with more ad­vanced cases of melanoma.

That old bot­tle is just fine.

Like spoiled milk, ex­pired sun­screen isn’t much good. But con­sumers seem be­fud­dled about whether an ex­pi­ra­tion date rep­re­sents a mean­ing­ful warn­ing or merely man­u­fac­turer cau­tion. Ac­cord­ing to one study, one-third of peo­ple don’t check the dates at all. Sun­screens ex­pire be­cause their in­gre­di­ents de­te­ri­o­rate over time, los­ing their power.

Old sun­block isn’t just in­ef­fec­tive; in some cases, that bot­tle in the back of the medicine cup­board might even be danger­ous: Ba­nana Boat was forced to re­call a raft of North Amer­i­can prod­ucts man­u­fac­tured be­tween Jan­uary 2010 and Septem­ber 2012 af­ter it was dis­cov­ered that th­ese posed a “po­ten­tial risk of . . . ig­nit­ing on the skin” if they came in con­tact with a com­bustible source (the fire from a bar­be­cue grill, say) be­fore com­pletely dry­ing. Be­sides, if you’re ap­ply­ing sun­block prop­erly, you prob­a­bly won’t have any left over at the end of the sum­mer, any­way.

Sun­screen is toxic.

“Your sun­screen might be poi­son­ing you,” de­clares a head­line on the Web site for “The Dr. Oz Show.” “Is sun­screen danger­ous?” asks U.S. News & World Re­port. Driv­ing th­ese wor­ries are past stud­ies link­ing par­tic­u­lar sun­screen in­gre­di­ents with un­de­sir­able byprod­ucts and pos­si­ble neg­a­tive health ef­fects. Some fear that it causes can­cer, though the med­i­cal con­sen­sus says such con­cerns are overblown. The link be­tween pho­to­dam­age and skin can­cer is well es­tab­lished; the pos­si­ble ad­verse ef­fects of sun­screen chem­i­cals far less so. And sun­block prod­ucts in the United States are rather well-reg­u­lated: The FDA has con­sid­ered sun­screen an over-the-counter drug since the late 1970s, mak­ing it sub­ject to more reg­u­la­tory scru­tiny than cos­metic lo­tions, fra­grances or creams that also pen­e­trate the skin.

This has drawn crit­i­cism from some quar­ters: Chem­i­cal & En­gi­neer­ing News re­cently lamented that Amer­i­can con­sumers do not have ac­cess to a num­ber of sun-block­ing in­gre­di­ents avail­able in Europe. Some of those com­pounds have been lan­guish­ing un­der FDA re­view since 2002. The pace of ap­proval is so slow that Pres­i­dent Obama signed the Sun­screen In­no­va­tion Act in Novem­ber 2014 to get things mov­ing.

But for those to whom “chem­i­cals” sound omi­nous and who dis­dain the thought of sun­screen, con­sider: Plant spores con­tain com­pounds that nat­u­rally block UV rays. Hip­pos se­crete a pig­ment mix­ture to pro­tect them­selves against the sun. We hu­mans would be fool­hardy not to learn from na­ture and do the same.


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