As the bounce wake up , more and more of us will be slathering on sunscreen before head outside to enjoy the weather condition . What SPF should we look for ? And what does that issue actually mean , anyway ? Let ’s resolve some sunscreen - concern questions .
To understand how sunscreen piece of work , it ’s important to first understand how ultraviolet light works .
UV visible light can be transgress down into three regions . UV - A rays have the long wavelength and are the nasty one that click deeply into the tegument ( down to your dermis ) to cause skin cancer and untimely aging . UV - B rays have a short wavelength and only reach the outer layer of the hide , the epidermis , but they ’re the major culprit behind sunburns . Then there ’s ultraviolet light - cytosine , which we do n’t really need to worry about ; the ozone layer , water supply vaporization , and other elements of the Earth ’s atmosphere absorb these ray before they can get down to us .
With that brief overview in mind, how does sunscreen work?
On two fronts . Inorganic compound like titanium dioxide and zinc oxide reflect or break up the ultraviolet illumination ray , while organic molecules like benzophenones ingest UV ray to keep them from reaching your skin .
SPF is calculated found on how much long it takes tegument treated with a sunscreen to sunburn compared to skin that has n’t been treated . Thus , a sun blocker with an SPF of 15 should theoretically allow a user to rest in the Dominicus 15 times as long before getting toasty . Put in more scientific terms , SPF 15 sunscreen blocks around 93 % of the UVB rays that would otherwise strike our skin , while SPF 30 blocks 97 % of the burn - causing UVB .
While these calculations are consistent – deed 21 , Part 352 of the Code of Federal Regulations depict a stringent methodology for fix SPF involve an “ accurately calibrated solar simulator ” – the numbers themselves can be a bit misleading . The factual amount of UV visible radiation that ’s reaching us when we ’re outside varies depending on factors like the fourth dimension of day , what ALT and parallel of latitude we ’re at , cloud covering fire , and reflection of UV irradiation by the dry land . ( The World Health Organization says snow can contemplate upwards of 80 % of the UV radiation that hits it , while beach George Sand can send back 15 % of beam . )
Thanks to these variant , it ’s hard to pinpoint a specific metre at which your SPF 15 or SPF 30 sunscreen will stop being effective . As a resolution , regardless of the SPF you ’re using , the FDA and other researcher advocate reapplying sunscreen at least every two hours or so . Moreover , the FDA and WHO advocate coupling sunscreen with other forms of sun protective cover , like clothing and spectre .
How much sunscreen should I put on? (Or: Why is there a picture of a sunscreen-filled shot glass above?)
Then there ’s another problem : even those of us who conscientiously hold sunscreen probably are n’t using enough ; many people are using as little as one quarter of the optimal amount of sunblock . How much sunscreen should you be using ? We ’ll cite the FDA because we love the imaging they use : “ An average - sizing adult or child needs at least one ounce of sunscreen , about the amount it read to fill a shot glass — to equally compensate the body from head to toe . ” contribute that to your list of reasons to take a blastoff glass to the beach .
