What SPF are you really getting in your sunscreen?

Image courtesy of Wikipedia user Axelv.
Image courtesy of Wikipedia user Axelv.

So what SPF (sun protection factor) should you really be using when you look for sunscreen?  The American Academy of Dermatology (AAD) recommends SPF 30 or higher.

But in a recent article by Yang, et al in the Journal of the American Academy of Dermatology (JAAD), researchers found that the actual SPF that is getting onto the skin is less.  Why is this? While we recommend to our patients to use 2 mg/cm^2 of skin (e.g. a shot glass full to cover the entire body), practically it gets applied unevenly and people use much less and don’t reapply the sunscreen as frequently as they should.  So, instead, these authors suggest that applying a sunscreen with higher SPF like 70+ is a good idea to account for potential under-application of sunscreen.  Interestingly, the cost of high SPF sunscreen is often about the same price as the lower SPF sunscreens, so hey, why not?