sunscreen protective factor index


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sunscreen protective factor index (SPF)

a system of evaluating the effectiveness of various formulations for protecting the skin from actinic rays of the sun. Protective agents are rated from 1 to 50 by the U.S. Food and Drug Administration. A sunscreen protective factor of 15 means that the sunscreen provides 15 times the protection of unprotected skin. Among the most highly rated sunscreen lotions are nonopaque combinations of paraaminobenzoic acid ester and benzophenone, parol 1789 with incoxide and titanium dioxide.

sunscreen protective factor index

In preparations for protecting the skin from the sun (using sunscreens), the ratio of the amount of exposure needed to produce a minimal erythematous response with the sunscreen in place divided by the amount of exposure required to produce the same reaction without the sunscreen. This index assesses the ability of sunscreens to block (short-wavelength) ultraviolet B rays but does not measure the protective effect of sunscreens against (long-wavelength) ultraviolet A radiation.
See: erythema dose
See also: index