If a shot glass full of sunscreen sounds like a lot of the lotion, you might not be used to applying enough of it.
"The average person, in studies, only applies approximately one-third of the sunscreen that is recommended by volume," says Dr. Dawn Davis, a Mayo Clinic dermatologist. "So, if you're wearing an SPF 15, unfortunately, you're only getting an SPF of 5 because of the way that you apply it."
And, she says, that a shot glass of protection mentioned earlier isn't enough to cover your whole body.
"A shot glass of sunscreen will only cover your face, your neck and the backs of your two hands," says Dr. Davis. "The average sunscreen bottle should only last you four to five full-body applications."
Besides rubbing on enough sunscreen, it's important to reapply it every two hours; even sooner if you're int he water, or if you are sweating.
"Even if your sunscreen is water-resistant, it is not waterproof." explains Dr. Davis.