What does SPF mean?

The SPF factor shows how much UVB radiation gets through during exposure to sun, provided that the right amount of sun protection is used. For example, SPF 10 allows 1/10 of the UVB rays through and therefore gives 90% protection while SPF 50 lets 1/50 through, which means it corresponds to 96% protection. It’s a common mistake to think that, for example, SPF 15 is twice as good as SPF 30, which is not true. SPF 15 gives 93% protection and SPF 30 almost 97%. Thinking you can stay in the sun 15 or 30 times as long is also incorrect. If you burn after 10 minutes, you can be out for 15 (SPF) x 10 (MINUTES) = 2.5 hours. This is also the total time you can expose the skin to the sun before it burns. This is assuming you apply the right amount of sun protection correctly as advised. With SPF 30 you should be able to stay in the sun for 5 hours in total if you re-apply properly.

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