Sun Protection Factor (SPF) – What Does It Mean To You?

With as high as SPF70 on the shelves, we don't blame you for thinking that you could hit the beach and tan for 12 hours without getting burned. The higher the number, the better, right? Before you throw caution to the wind, though, you should know a few things about SPF. What is it, exactly? What do the numbers mean, and how high can they go?

We use sunscreen to block ultraviolet light from damaging the skin. There are two categories of UV light - UVA and UVB.  UVB causes sunburn, and UVA has more long-term damaging effects on the skin, like premature aging.

To figure out how long you can stay in the sun with a given SPF, use this equation:

Minutes to burn without sunscreen x SPF number = maximum sun exposure time

For example, if you burn after 10 minutes of sun exposure, an SPF of 15 will allow you to be in the sun for up to 150 minutes without burning. But people usually use far less amount of sunscreen that is actually required. In the real world, the average sun worshipper uses half the amount of sunscreen used in the laboratory, which could result in a sunburn in half the time.

Also, despite waterproof or sweatproof labels, all sunscreens decrease in effectiveness when exposed to water or sweat. If you don't apply the correct amount and then reapply after exposure to water, a 12-hour bake in the sun could give you a very serious sunburn.

Protecting yourself:

1. Know thyself:  If you are whiter than a sheet of paper, if your Aunt Mary has skin cancer, or if you are sensitive to the sun because of a medication or a medical condition, take extra measures. Stay out of the sun as much as possible, wear a hat when you are out, use a broad-spectrum sunscreen with a high SPF and reapply that sunscreen often.

2. Broaden your spectrum: The SPF number indicates protection only against UVB rays -- many sunscreens, even those with a high SPF, allow UVA rays to be absorbed by the skin. UVA protection is usually indicated by a "broad-spectrum" label. Look for this to ensure the most well-rounded sun coverage.

3. Here comes the sun: To be effective, sunscreen needs to be fully absorbed into the skin, so apply it 15 to 30 minutes before you even step into the sun.

4. Reapply yourself: Whether you're lying by the pool or cycling around, you'll probably be exposed to sweat or water, the natural enemies of sunscreen. To be safe, reapply after you swim or sweat.

5. Full exposure: No matter how high the SPF, sunscreen can protect only the skin it covers. The most commonly missed spots are the temples, ears, back of the neck and top of the feet. If you are sometimes guilty of losing your focus while applying your lotion, try one of the sunscreens that contains disappearing colorants, so you can identify unlotioned areas before they burn to a crisp.