It’s summer where I am, and I spend most of my day outside. So I put on a fair amount of sunscreen. But as my sister said something about only wearing SPF 70 and not SPF 30, I wondered what exactly SPF is, and more importantly what it means.
I decided to look it up. SPF stands for Sun Protection Factor. It turns out that the SPF number is the amount of times longer you can stay out in the sun without getting burned. So let’s say you go lay in the sun without any sunscreen on and you burn in ten minutes. If you went out wearing SPF 30 sunscreen, you should technically be able to lay in the sun for 30 times as long, or 300 minutes, before getting burned. Some people believe that higher SPFs protect more, but it turns out that SPF 70 blocks about 2% more radiation than SPF 30.
Sunscreens protect against damaging ultraviolet rays, which are a type of invisible light. There are UVA rays, which cause premature aging, wrinkles and skin cancer. They penetrate deep into the skin. And there are UVB rays, which cause burning and also premature aging and skin cancer, but they mostly affect the top layers of skin. The third type of UV radiation is UVC, which is completely absorbed by the ozone layer. Broad spectrum sunscreens are the ones that protect against both kinds of UV radiation.
Based on what you’ve just read, you may be wondering why you can’t go sit out in the sun for five hours with SPF 30 on without getting sunburned. You aren’t alone. It turns out the reason most people get sunburned or have their skin permanently damaged is not that they don’t wear sunscreen, it’s that they don’t wear enough. When SPFs are tested for, the test subjects have an ounce of sunscreen on their bodies. So for your SPF 30 to work to its full potential, you real need to pour it on. You also have to (this is the part everybody hates) reapply. Between sweating and the water, you lose a lot of sunscreen throughout your day at the beach, so it is important that you reapply every couple hours or after getting out of the water.
So there you have it! The general explanation of what an SPF number means. So don’t worry too much about what number is on the bottle, just make sure that next time you’re out in the sun you really glob on that sunscreen!