I have heard that SPF 15 is about as high protection as you can get, why is this?
This is absolutely true. SPF 15 equates to 93.3% UV absorption, which means by applying such a product 93.3% of the UV your skin would otherwise be absorbing is getting absorbed by the product. Doubling the SPF value to 30 provides 96.7% UV absorption, or only 3.4% more UV protection with a possible 100% more petrochemical exposure, and this only works as long as the product stays on your skin, which sunscreens don’t do well. Each additional SPF unit above SPF 15 provides only a fraction more protection, but significantly more petrochemical exposure. Take a look at this graph. If it isn’t on your skin, even an infinite SPF won’t do you any good.
It is for these reasons that the American Academy of Dermatology recommends you use an SPF 15 sunscreen and reapply about every two hours, or more often if you swim, sweat or even roll over on your towel.
The graph above was mathematically derived by our founder, Erik Kreider, however afterward we discovered it was also published originally by RM Sayre, in Photochemistry & Photobiology, 1979. An interesting paper on UV and sunscreens that cites Sayre can be found here: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3460660/.
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