Patent ID: 7567080

Claim:
A method for determining an integral sun protection factor (∫ SPF) encompassing both UVA and UVB radiation for cosmetic and dermatological sunscreens, which method comprises the steps of (a) applying a defined amount of a sunscreen directly onto a defined area of a skin substrate which has been impregnated before with a known substance acting as a spin trap, (b) exposing the skin substrate to a defined amount of radiation comprising UVA and UVB rays according to natural sun exposure conditions by means of a radiation source, (c) subjecting the skin substrate exposed to radiation to an electron spin resonance (ESR) measurement within 1-120 minutes after exposure, (d) normalizing a free radical generation value RG once it has been compared with a standard sample whose number of free radicals is known, and recording a number of free radicals trapped as a real number X multiplied by 10 12 per 1 mg of sample, RG=X×10 12 free radicals/mg of skin sample, (e) and determining the integral sun protection factor ∫ SPF according to the equation (1) ∫ S ⁢ ⁢ P ⁢ ⁢ F = E 0 E , ( 1 ) wherein E 0 has a meaning of UV dose supplied to the skin sample in mJ/cm 2 on which the sunscreen was applied and is calculated in equation (7) E 0 =I·t (7) I=sun simulator irradiance (mW/cm 2 ) t=exposure time in seconds, and E has the meaning of effective UV dose in mJ/cm 2 , so related to the detected amount of free radicals generated during step (b) and wherein log 10 E is calculated according to the real number X of free radical generation value in step (d) with equation (2) log 10 ( E )= a ·log 10 ( X· 1000)+ b (2) in which the number of free radicals is not proportional to the UV dose and wherein a and b are experimental parameters which have been determined in an adjustment step to achieve a correct linear relationship between logarithm functions to the base ten of UV dose and real number of free radical generation through square error assessment method, and E is calculated according to equation (8) E= 10 log 10(E) (8).