Slather on the sunscreen and you’ll be protected from a blistering burn, right? Not always.

The “margarita burn” is well known, but there are other things that can decrease the effectiveness of sunscreen that you may not know about.

It’s important because even one blistering sunburn during childhood or adolescence can nearly double the risk of developing melanoma. Five or more sunburns between the ages of 15 and 20 can increase your skin cancer risk by as much as 80 percent, according to the American Dermatology Association.