A sunscreen labelled "SPF 15" should let you spend about 15 times as long in the sun before you burn. Pretty awesome, right? Unfortunately, most of us don't get that level of protection because we don't apply enough. What you're likely getting: a mere SPF 2.
Photo by haiderzs.
We should be using about 30mL of sunscreen, or almost a shot glass full, to get the recommended 2mg per square centimetre of skin. That's what the label's SPF — short for "Sun Protection Factor" — is based on. However, most of us use a lot less. According to some studies, the average person uses between 20 per cent and 50 per cent of the recommended amount. That means we're not getting the protection we think.
Here's a handy chart from the Environmental Working Group's sunscreen tests:
|SPF on label||Average SPF of users (25% of the recommended amount)|
So if you're thinking that the SPF 100 protects you much better than the SPF 15, it doesn't — unless you apply the recommended amount. Read more at the link below about the science behind choosing a good sunscreen.
The Great Sunscreen Cover-Up [Science Based Medicine]