What does SPF stand for on suntan lotion bottles and how does it protect us from the sun?
The SPF (sun protection factor) of a sunscreen is a laboratory measure of the effectiveness of sunscreen; the higher the SPF, the more protection a sunscreen offers against UV-B (the ultraviolet radiation that causes sunburn) and UV-A (more associated with longer-term skin damage). The SPF indicates the time a person can be exposed to sunlight before getting sunburn with a sunscreen applied relative to the time he or she can be exposed without sunscreen. Most sunscreens work by containing either an organic chemical compound that absorbs ultraviolet light (such as oxybenzone) or an opaque material that reflects light (such as titanium dioxide, zinc oxide), or a combination of both. Typically, absorptive materials are referred to as chemical blocks, whereas opaque materials are mineral or physical blocks. http://en.wikipedia.
