Eli5 – Why would one choose SPF30 (or less) when SPF50 sunscreen is widely/readily available?
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There’s a number of reasons. First off higher SPF sunscreens are generally more expensive. In addition they tend to be greasier, smell more, can be a bit more difficult to spread, and can irritate sensitive skin.
In addition the benefits of a higher SPF are not as big as you might think, SPF 30 sunscreen filters out 97% of UVB rays, SPF 50 filters out 98%, and SPF 100 filters out 99%. Unless you have certain skin or immune conditions, or a history of skin cancer, there isn’t really *that* big of a difference.
There is also some evidence that higher SPF sunscreens can actually *increase* your UV exposure because people overestimate their effectiveness and skip reapplication. You need to reapply sunscreen every 90 to 120 minutes and after you get out of the water or finish activities where you are sweating, regardless of what SPF you use.
Further it’s not just about SPF. There are two kinds of UV rays: UVB and UVA. UVB is primarily responsible for sunburns, while UVA is responsible for skin aging. Both increase your risk of skin cancer. SPF measures how effectively a sunscreen filters out UV*B* rays, if you’re also looking for protection from UV*A* rays then you need a “broad spectrum” sunscreen. So a SPF 30 broad spectrum sunscreen will actually offer better protection than a SPF 100 that is not broad spectrum.
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