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What Do the Numbers on Spf Mean?
SPF stands for ‘sun protection factor’ and the numbers following (for example SPF30 or SPF50) refer to how well the product will protect your skin against sunburn.
A simple formula is used to calculate the SPF number – the number of seconds that it takes a patch of skin to slightly redden when covered in sunscreen divided by the number of seconds it takes to slightly redden with no sunscreen.