I know what you're thinking: Who doesn't know what SPF is? But the truth is that every time I quiz a group of gals about their sun smarts, there's inevitably an unsure shrinking violet in the corner. I thought this would be the perfect chance to clarify what the SPF in all of the sunscreen-related beauty products actually means.

SPF, short for Sun Protection Factor, is a number that, according to the FDA, must be apparent on all sunscreens. The number indicates how long you can be exposed to the sun without turning red. For example, if you are someone who burns after 10 minutes and you apply SPF 15, then you will be shielded from turning red 15 times longer than if you didn't apply sunscreen.

Naturally, the higher number SPF you use, the more protected you'll be — and if you have fair skin, you'd be advised not to use anything less than SPF 50. It is also important to understand that sunscreens protect you by absorbing UVB and/or UVA rays. Most sunscreens shield against UVB rays, but if you really want to be sun savvy, I suggest reading the packaging carefully to ensure that it also offers UVA defense.