But what's with those numbers? The sun protection factor, or the SPF, ranges from a low of 2 to a high of 50 and sometimes higher. Most of us understand that the SPF has something to do with providing protection from the sun's damaging ultraviolet rays. But beyond that, the number is shrouded in mystery.

What does SPF mean?

The SPF is a comparison of the time it takes before the skin will start to redden with and without sun protection. In addition, SPF pertains only to UVB rays, the ones that cause tanning but also sunburns.

For example, if it would take 20 minutes for an individual's skin to burn without sun protection, then a SPF of 15 means that when applied, that person can remain in the sun 15 times longer, or up to 5 hours, without worrying about burning. The greater the SPF, the longer the protection it offers, but only up to a certain point. SPFs greater than 15 offer only small increments of additional protection. And that's the theory behind the SPF.

In reality though, sun protection regardless of SPF becomes less effective when it's not evenly applied, a person goes into the water and a person sweats. Both water and sweat diminish the product's effectiveness that's why it's extremely important to reapply sun protection frequently.

Besides reapplying, for maximum effectiveness the first application should happen approximately 20 minutes prior to going out into the sun. Doing so allows sufficient time for the product to fully absorb into the skin. It also ensures that you'll be protected the moment you step outside.

Which SPF is right for me?

For most people, sun protection with a sun protection factor of 15 provides adequate protection as long as it's frequently reapplied. However, those with more sensitive skin will benefit from a higher SPF. People who are fair-skinned, have light-colored or red hair or who are traveling to certain high altitude or tropical destinations will also benefit from a higher SPF. Those with darker skin generally don't burn as easily and need only a mild SPF. When choosing remember that a higher SPF does not offer more protection - it offers longer protection.

Other sun protection products

Self-tanning products and bronzers are safer ways to color your skin because the skin isn't being exposed to ultraviolet radiation which over time damages the skin's cells. These products don't offer sun protection unless the label specifically states otherwise by listing a sun protection factor. But remember that a sun protection factor corresponds to a period of time and therefore, even if the product offers sun protection, it's not going to last until you wash the product off in a few days.

Do not be confused between SPF, UPF, and EPF. As explained above SPF (sun protection factor) refers to sunscreens; UPF (ultraviolet protection factor) refers to sun protection swimwear, UV protective clothing and sun protection hats; EPF (eye protection factor) refers to sunglasses. Next time you purchase your sun protection product make sure you ask for SPF, UPF, or EPF certification.