What do SPF ratings mean?
I was out in the sun ALL DAY yesterday. Of course I applied sunscreen in the morning before I left the house... but I didn't reapply, so my face and shoulders are feeling a little tight this morning. I used SPF 30... but what does that even mean?
The SPF number tells you how long the sun’s UV radiation would take to redden your skin when using the product exactly as directed versus the amount of time without any sunscreen. So ideally, with SPF 30 it would take you 30 times longer to burn than if you weren’t wearing sunscreen.
An SPF 30 allows about 3 percent of UVB rays to hit your skin. An SPF of 50 allows about 2 percent of those rays through. That may seem like a small difference until you realize that the SPF 30 is allowing 50 percent more UV radiation onto your skin.
Under ideal conditions (like in a laboratory), a sunscreen with higher SPF protection and broad-spectrum coverage offers more protection against sunburn, UVA damage and DNA damage than comparable products with lower SPF values. But, in real life, products with very high SPFs often create a false sense of security. People who use them tend to stay out in the sun much longer. They may skip reapplying. And they may think they don’t need to seek shade, wear a hat or cover up with clothing. They end up getting a lot more UV damage, which, of course, defeats the purpose.