Be honest: Do you understand how your sunblock works? Or rather, do you understand the meaning of that telltale number on the bottle? Is SPF 15 really any better than SPF 50, and how can you tell the difference?
Well, to answer your questions, sunblock works like this: Say you're pretty fair, and when you go outside, your skin starts to burn within about 10 minutes in direct sunlight. So, you reach for a bottle of SPF 15 sunblock. What does that get you?
"It gets you 15 times more protection than not wearing any sunblock at all," says Henderson, Nevada, plastic surgeon Dr. Ryan Mitchell. "And SPF 50 would get you 50 times more protection than no sunblock. But that means time - not coverage."
So, if it took you 10 minutes to burn with no sunblock, wearing SPF 15 would essentially buy you 15 times longer – or 150 minutes - in the sun, and SPF 50 would get you about 500 minutes, right?
Well, not quite, says Mitchell.
"The thing is, SPF doesn't take many things into account, such as the activity level of the wearer - whether they're in the pool, playing a sport, or even sitting completely still and sweating. All those things can make your sunblock wear off faster, even if it's called waterproof or sweat-proof," he says.
So, what can you do if there's no exact science to when and what to apply? The good news is that question has been answered for you, in the form of a new tool called the Sunbathing Calculator, developed by Dr. Malgorzata Koperska of Omni Calculator.
The Sunbathing Calculator takes sun protection even further, by factoring in SPF, elevation, sunlight intensity, skin color, if you are near water or snow (both reflective, and thus sun-intensifiers), and the amount of time you plan on spending outside. Once you input that information, the Sunbathing Calculator generates a number in hours and minutes that you can safely stay outdoors before burning - provided you are honest about your answers.
So, what do doctors like Mitchell think of the Sunbathing Calculator?
"It appears to be an excellent tool for getting an accurate idea of how long you can expect your sunblock to last. However, don't forget to take factors like sweat and water into account," says Mitchell. "And do yourself a favor - Google the elevation of your location. Here in Henderson, we are at 1,867 feet, but if you take a trip to Lake Tahoe, California, you're at 6,225 feet. Long Beach, California, is only 52 feet! So changing the settings can make a drastic difference in results - and ignoring them could cause some problems."
The Sunbathing Calculator can be found here: https://www.omnicalculator.com/other/sunscreen.