SPF is an abbreviation for Sun Protection Factor which is a simple aid to help tell you how effectively a sunscreen protects you from the UVB rays of the sun in causing sun damage. We have three different sunscreens here, with SPF’s from 15 to 60. The SPF rating tells you how long you can stay out in the sun without getting sunburn with that sunscreen, compared to how long you could have stayed in the sun before you burned without a sunscreen. For instance if it normally would take you about 15 minutes to start to get a sunburn if you didn’t wear any sunscreen and you used an SPF with a number 2, then it would take you twice as long, or 30 minutes before you would start to burn. And similarly, if you used an SPF with a value of 10, it would take you 10 times 15 or 150 minutes, or 2 and a half hours before you start to get a sunburn. That’s all there is to it. Of course we learned that in order to get that full SPF protection you need to reapply your sunscreen frequently and you need to apply enough each time you put it on. But there’s one more important factor to consider, when we first started using SPF or Sun Protection Factors, more than 30 years ago, we thought that the only ultra-violet rays that cause damage from the sun were these shorter UVB rays. But we’ve since learned that the longer UVA rays also cause damage. They cause premature aging of the skin as well as contributing to skin cancer. So, when you buy the sunscreen with the specific SPF value, and I recommend 15 to 30, keep in mind that’s only telling you about protection from the UVB rays. The sunscreen also needs to be labeled with UVA protection or broad spectrum protection to make sure that additionally you are getting protection from all the damaging ultra-violet rays from the sun.