SPF stands for sun protection factor. Sunscreens are rated or classified by strength of their SPF. The SPF numbers on the packaging can range from as low as 2 to greater than 50. These numbers refer to the product's ability to deflect the sun's burning rays.

The sunscreen SPF rating is calculated by comparing the amount of time needed to produce sunburn on sunscreen-protected skin to the amount of time needed to cause a sunburn on unprotected skin. For example, if a sunscreen is rated SPF 2 and fair-skinned person who would normally turn red after ten minutes of exposure to the sun uses it, it would take twenty minutes of exposure for the skin to turn red.

A sunscreen with an SPF of 15 would allow that person to multiply that initial burning time by 15, which means it would take 15 minutes longer to burn, or 150 minutes. It is strongly recommended that one use a broad-spectrum sunscreen with an SPF of 15 or greater year-round for all skin types.

I. Ricardo Martinez, M.D., Ph.D., is Chief of Dermatology at East Jefferson General Hospital. To make an appointment with Dr. Martinez or another physician at EJGH please call HealthFinder at 456-5000.