I have heard that SPF 30 is about as high protection as you can get, why is this?
This is absolutely true. SPF 30 equates to 96.7% UV absorption, which means by applying such a product 96.7% of the UV your skin would otherwise be absorbing is getting absorbed by the product. Doubling the SPF value to 60 provides 98.3% UV absorption, or only 1.6% more UV protection with a possible 100% more petrochemical exposure or more, 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 30 provides only a fraction more protection, but significantly more petrochemical exposure. Take a look at this graph. And 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 30 sunscreen and reapply about every two hours, or more often if you swim, sweat or even roll over on your towel. However, the reapplication advice is most appropriate for petrochemical sunscreens, as they degrade and become ineffective with exposure to sunlight and heat. Zinc oxide doesn’t degrade in this way, so unless you’ve done something to remove it from your skin, reapplication isn’t as necessary.
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/.
Like what you’re reading? Try our zinc oxide Sunscreens!
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