Anatomy of a Sunscreen

Not sure how to decipher your sunscreen bottle? Here's some help.

There’s nothing worse than grabbing a cheap bottle of sunscreen on your way out the door to the slopes, half-slathering it on as you squirm into your ski boots, and ending up with painful après-ski raccoon eyes because your sunscreen was only SPF 2. Here’s our glossary so you can interpret your sunscreen bottle before application.

SUNSCREEN chemically absorbs UV rays (as with the active ingredient avobenzone).

SUNBLOCK physically deflects UV rays (as with titanium dioxide). Sunscreen and sunblock can be equally effective, but neither offers complete protection. A new FDA regulation will eliminate the use of the word “block” from sun-safety products; many feel the term is misleading because nothing truly blocks or absorbs all UV rays. This new regulation will not become official until 2002.

SPF: Sun Protection Factor. SPF is calculated by comparing the amount of time it takes to produce a sunburn on protected vs. unprotected skin. For example, a person wearing SPF 15 will take 15 times longer to burn. That means the amount of UV blocked doesn’t increase proportionately with SPF: An SPF of 30 means 97 percent of sunburning rays are absorbed or deflected. SPF of 2 means 50 percent absorption or deflection. SPF only measures protection from UVB rays and the low end of the UVA spectrum. There is no official standard that measures protection against all UVA rays.

UV: Ultraviolet rays, which are a stream of invisible high-energy rays from the sun.

UVB: Ultraviolet B (rays associated with sunburn; they do not penetrate glass).

UVA: Ultraviolet A (rays associated with cell damage because they penetrate beyond the top layer of skin, as well as through glass).

BROAD-SPECTRUM: Protects from the full spectrum of UVB and some UVA.