2. But, how you apply matters more. Apply a shot-glass worth every hour
According to a dermatologists The Sweethome spoke to as well as multiple academic papers and studies they referenced, you should apply a shot-glass-size worth of sunscreen (or about an ounce) every hour that you're outside. According to the research, most of us only use about a quarter to a half of what is actually needed to receive the advertised SPF benefits.
To make the most of your sunscreen, you should apply at least 30 minutes before you go outside, then once again each hour and every time after you swim and/or sweat. Sound like a lot of lotion? It is. Which means the more affordable your sunscreen the better.