SPF simply stands for Sun Protection Factor. It is a measure of how protective a sunscreen is against UVB rays. It does not measure the protection against UVA rays. Find out more about UVA vs. UVB rays.
Theoretically a SPF 15 sunscreen will allow you to be in the sun 15 times longer before you would burn than without any sunscreen at all. Put simply if you would burn in 10 minutes without any sunscreen then with an SPF 15 sunscreen applied (in the correct amount) you could spend 150 minutes out in the sun without burning (that’s 10×15=150 minutes).
Now where it gets a little tricky and possibly sounds a bit misleading is the difference in sun protection between the varying SPF levels. So let’s break it down:
- SPF 15 filters out approx. 93% of all incoming UVB rays
- SPF 30 filters out approx. 97% of all incoming UVB rays
- SPF 50 filters out approx. 98% of all incoming UVB rays
Now you can see that an SPF 30 does not provide twice as much protection as a SPF 15.
The general consensus is that a SPF 15 sunscreen is adequate for most people. However, if you are particularly fair skinned, have had skin cancer or have a family history of skin cancer or if you are particularly sensitive to light (as happens with some medical conditions or in people taking certain medications) then you should choose a SPF 30 or higher sunscreen.
Please keep in mind that all testing is completed in controlled environments with the correct amount of sunscreen applied.
Find out How Much Sunscreen To Apply
Find out about UVA vs. UVB Rays & What Does Broad Spectrum Mean?