Part 4 of 4: Does using an SPF greater than 30 make a difference?
The answer to this question depends on how much sunscreen you apply. In a prior blog post, I defined the SPF value. Another way of defining SPF is to think about the fraction of the sun’s light that is filtered out with each SPF value. An SPF of 30 allows 1/30 of the rays to reach your skin which is equivalent to blocking out 29/30 or 97% of the rays and an SPF 50 blocks out 98% of the rays (only a 1% increase from spf 30), so the percent difference between these SPF values is not huge. In theory, using an SPF of 30 would block out about 97% of the sun’s rays and that sounds pretty good, right?
However, in order to achieve the SPF on the bottle, you have to apply about a shot glass full of sunscreen to your body with each application. Most of us only apply about 1/4 to 1/2 of the recommended amount of sunscreen, so we do not achieve our goal of an SPF of 30. A study published in the Journal of the American Academy of Dermatology in 2012 found the sunscreens with an spf of 70 or greater provided adequate protection when used in a typical fashion (applying about 1/4 of the amount used in traditional SPF testing). Another study also published in 2012 showed that consumers who applied 2 coats of sunscreen prior to sun exposure obtained adequate protection from the sun when using an SPF of 30 or greater.
Key points to remember from this series:
- Sun protective clothing is easier to use and more effective than sunscreen at protecting your skin from the sun’s radiation
- You should reapply sunscreen every 2 hours when you are out all day to maintain adequate sun protection
- Sunscreen used on a daily basis should be broad spectrum (contain zinc or avobenzone) to protect from the sun rays that lead to photo aging even when you are less concerned about sunburn
- To get adequate protection from the sun, use SPF 70+ or apply two coats of SPF 30