Sunscreen bottle in beach sand

Myth No. 3: SPF 30 is twice as protective as SPF 15

Third grade was great, wasn't it? We got to play dodgeball, there were milk breaks, and 15 plus 15 equaled 30.Don't worry: It still does, but third grade math does not apply to sunscreen. An SPF 30 sunscreen does not deliver twice the protection of an SPF 15 sunblock.

If you're shelling out a couple extra bucks for SPF 30 thinking you're getting extra protection, you are -- but not as much as you think.

SPF 15 blocks about 96.7 percent of UV rays. SPF 30, on the other hand, blocks 97.7 percent of those rays. That's right. That extra money buys you a measly 1 percent (and a false sense of security). And as you move up the scale (SPF 40 and 50, for instance) the number barely even changes.

Save up those couple bucks and invest in a hat.