34. 30 is the Magic Number
SPF 15 feels like a sound option to make, but you’d be surprised that that’s not going to do anything for you. Most doctors recommend at least SPF 30 or higher if you want to prevent sunburns from occurring.
This advice is because SPF 30 blocks half the amount of radiation as SPF 15, meaning that you’re less likely to get burned. You will have to reapply it every two hours or so to maintain the same level of protection, however, so take your sunblock with you if you’re away from home.