When it comes to sun protection, a little dab of sunscreen won't do ya.

To get the full sun protection factor (SPF) that's printed on the bottle, you have to use the amount that scientists use in testing. For most sunscreens, that's about 2 mg/cm². Here's how much that is in plain English.

Here are three key sunscreen ingredients . . .

Sunburn Safeguard
Most of us use only about a quarter of the sunscreen quantity needed to get the full SPF protection advertised on a label. To get the full benefit, you need to slather on a lot of the stuff -- about 2 milligrams of product per square centimeter of skin.

That translates roughly into about two finger-length squirts of the sunscreen applied to every major body area (head/neck/face, left arm, right arm, upper back, lower back, upper front torso, lower front torso, left thigh/knee, right thigh/knee, left lower leg/foot, right lower leg/foot).

Feel like you're swimming in sunscreen? Good. You're on the right track.

Now, brush up on what UVA, UVB, sun sensitivity, and SPF all mean with this article.