Is the number on suncreen an indicator of how long it lasts, how much sun it can take or the percentage of rays it blocks? Or is it something else entirely?
In: Chemistry
Assuming you mean the SPF number, it’s a measure of how much UV light is blocked by a fixed layer of cream. A cream with an SPF of X will let through 1/X of the UV light hitting it and therefore let you stay out X times longer before getting a given dose of UV.
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