un rotection actor. A world-wide rating system for measuring the amount of protection from ultraviolet radiation that a sun lotion gives.

SPF measures the effectiveness of sunscreen on the body. the test for SPF is done by using a living organism or body to measure the length of time it takes for the skin to redden without coverage or protection.

Scale for rating sunscreens. Sunscreens with an SPF of 15 or higher provide the best protection from the sun's harmful rays.

Sun Protective Factor

SPF is the ratio between the lowest amount of UV energy required to produce minimal redness in sunscreen-protected skin to unprotected skin, although it is often interpreted as the ratio of time taken to burn in protected versus unprotected skin

A number by which sunscreen users can determine the duration of effectiveness simply by multiplying the SPF by time it takes them to burn without sunscreen.

Sun Protection Factor.

Number representing the amount of sun something blocks. For example, if you normally begin to burn after half an hour in the sun, a sunscreen with an SPF of 2 should let you stay out twice as long (1 hour), SPF 4 should let you stay out four times as long, and so on.

The numerical rating system used on sunscreens and sunblocks, which indicate the level of protection that they can provide to the skin from ultraviolet light. The higher the SPF, the greater the protective capacity.