Sun Protection Factor is simply an equation for measuring what percentage of UVB (not UVA) rays will be blocked. The equation is (SPF-1)/SPF = “Percent UVB Blocked”.
So…SPF 53 blocks 98% of the sun’s rays (52/53 = 98.1%).
Where does that leave us? Well to figure out how long you can stay in the sun, you need to figure out how strong the sun is (look at the UV Index) and how sensitive your skin is. Here’s how it works: take the time it takes your skin to get pink without protection, and multiply that number by the SPF. If it takes 10 minutes, then an SPF of 53 will keep you from getting pink for 530 minutes, or a nearly 9 hours – if it stays on your skin completely the entire time.
Not sure how helpful that is. Who wants to go out and see how long it takes to burn (since that involves letting yourself burn)? And there are a bunch of problems with the equation. First, the strength of the sun changes all day long. Second, in order to get full SPF protection, the sunscreen has to be applied in sufficient amount and works only if it doesn’t wash or rub off (a huge “if” for many sunscreens). Third, SPF only relates to UVB rays and burning…UVA may be causing real harm without your sunscreen lifting a finger to help and without you even knowing it.
For all of these reasons, and others, the CDC recommends erring on the side of caution. SPF isn’t meaningless, of course. The FDA and EPA recommend using an SPF of at least 15. We agree. We,and others, think you should also use a sunscreen that blocks UVA light and stays put when you don’t. And given recent research on common synthetic sunscreen agents, keeping it natural is a good thing, too! Did we mention Sana’s sunscreens have the highest natural SPF on the market, full UVA protection, the highest level of water resistance, and no synthetic ingredients at all? That’s what we call erring on the side of caution!
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