Sun protection goes the distance

摘要

Sun protection products are unique in cosmetic compositions in that claims for their efficacy are quantified numerically as sun protection factors (SPF) and these must be proven. Final SPF testing is an in vivo procedure whereby 2mg/cm~2 of product is applied to the back of a subject, who is then exposed to UV radiation. SPF is defined as the minimal erythema dose (MED) in sunscreen-protected skin divided by the MED in non-sunscreen-protected skin. The MED of UV radiation is that required to produce a minimal skin erythema, expressed in joules per square centimetre (J/cm~2).