Perplexed by the claims plastered across that bottle? We asked dermatologists Cheryl Karcher and Francesca Fusco to demystify the labels:

What is SPF?
The number measures how long the formula resists UVB rays, the ones responsible for sunburns and skin cancer. If your skin normally starts to burn after 10 minutes of sun exposure, a liberally applied coat of SPF 15 will multiply that time by 15, giving you 150 minutes of UVB protection. But this number tells you nothing about UVA, the rays that prematurely age the skin and also cause cancer. To shield yourself from both, choose a formula that’s labeled broad spectrum.

What’s in this stuff?
Chemical blockers, like avobenzone and Mexoryl, absorb harmful UVA and UVB rays. These ingredients blend readily into the skin, leaving no white residue, but they may irritate sensitive complexions and can degrade in the heat: regular reapplication is crucial. Physical blockers, like zinc oxide and titanium dioxide, sit on the surface and reflect damaging rays. They’re ideal for tempermental skin and for kids but may feel pasty or clog pores.

How long will it last in the tube?
The FDA requires that sunscreens retain their original strength for three years, but storing them in hot glove compartments or on sunny beach towels can weaken them more quickly. To be on the safe side, toss your sunscreen if its color or consistency changes, or if you have any left over on the tube when summer is over.

And on my body?
No sunscreen is waterproof. Scan the bottle for the term water resistant, which indicates that the formula will remain effective for 40 minutes of swimming or sweating. (That time increases to 80 minutes if the tube reads very water resistant.) No matter wat the laberl says, it’s important to reapply SPF periodically according to the directions.

Still confused?
Sunscreen labels will be a bit less cryptic come December, when the FDA’s new regulations go into effect. (Smaller manufacturers have until the end of 2013 to comply.) Among the most important changes: Only broad-spectrum sunscreens with an SPF of 15 or higher can claim to reduce the risk of cancer and early skin aging.
For more on the rules visit Parade.com/sunscreen.
Source: Cleveland Plain Dealer Parade Magazine 6-24-2012