How do you read the numbers on sunscreen? The SPF numbers are determined in a lab. The number associated with SPF shows how much UVB light sunscreen can filter out. For example, SPF 15 covers 93 percent of the sun’s UVB rays, and SPF 30 covers 97 percent of the sun’s UVB rays. The higher the SPF, the more sunburn protection a sunscreen offers.
What leaves white cast in sunscreen? The UV filters in sunscreen, primarily the titanium dioxide and zinc oxide components in physical sunscreens, give it a “white cast.” Some sunscreens can make your face appear lighter than your neck, streak, or leave a white residue on your skin after application.
What does the number on sun screen mean? What Does the SPF Number 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.
How much sunscreen is in a teaspoon? That translates to half a teaspoon on face and neck combined — a quarter teaspoon each — and 1 teaspoon per arm and leg each, front and back,” says board-certified dermatologist Ranella Hirsch. “Realistically, people use somewhere around half of that amount.”