No SPF, not even 100+, offers 100 percent protection. SPF only rates UVB protection, but both UVA and UVB radiation can lead to skin cancer, which is why dermatologists now advise using sunscreens with an SPF of at least 30 but look carefully to make sure the sunscreen gives UVA protection too, there is currently no rating system in the US for UVA protection.
The difference in UVB protection between an SPF 100 and SPF 50 is marginal, SPF 100 does NOT offer double the blockage,
SPF 100 blocks 99 percent of UVB rays.
SPF 50 blocks 98 percent of UVB rays.
SPF 30, blocks 96.7 percent of UVB rays,
A sunscreen’s SPF number is calculated by comparing the time needed for a person to burn unprotected with how long it takes for that person to burn wearing sunscreen. So a person who turns red after 20 minutes of unprotected sun exposure is theoretically protected 15 times longer if they adequately apply SPF 15.
A lot of sunscreens rub off and degrade with time which is why dermatologists advise reapplication every two hours or after swimming or sweating.
Consumers should worry more about wearing enough sunscreen.
Skimp and you lose. To get the SPF advertised, you must use a full shot glass on your body. That’s an ounce, which means a three-ounce tube should last, at most, a few outings.
The biggest danger is people tend to think if they use a sunscreen labeled 100 then they can use half the directed amount and receive a protection factor of 50 but this is not the way the rating works
It turns out that if you apply half the amount, you get the protection of only the square root of the SPF.
Applying a half-ounce of SPF 70 will not give you the protection of SPF 35, but 8.4 and not necessarily give any protection from UVA!
Above SPF 50 lulls consumers into a false sense of security. Put SPF 100 on your kids at dawn, and you might think, “Great, they are covered all day” but the same 2 hour rule still applies no matter how high the SPF number.
Today is the last day of ‘Skin Cancer Awareness Month” but it’s only the beginning of summer.