Establishment and application of a pigmentation model induced by low dose ultraviolet in human skin

Objective To establish a pigmentation model in human skin by repeated low dose ultraviolet and to assess the whitening efficacy of a whitening product by this established pigmentation model.Methods Buttocks of 20 subjects were exposed to ultraviolet.Three consecutive daily UV exposures were performed as follows:Day 1 = 1MED,Day 2 = 0.5MED,Day 3 =0.5MED.The whitening product was applied twice per day on the exposed areas from Day 1 to Day 27.CM2500d chromameter,Maxmeter MX18 and visual evaluation were used to assess the change of skin color.Results The measurement of the pigmentation model showed that L value declined abruptly at Day 3(P0.05) and then slowed down and reached to a lowest point at Day 6.It then almost stayed at the same level until Day 20,thereafter it increased slowly.The b value showed little decrease during the first three days.It then increased persistently until to Day 27.The melanin index(M) also did not increase significantly during the first three days.It kept persistent increase until Day 20.At Day27,it showed little decrease.On the other hand,a and erythema index(E) increased abruptly during the first three days,peaked at Day 6 and then slowly declined.A whitening product was assessed by this pigmentation model.It was found that △L、△b and △M of the whitening product were lower than those of vehicle,but no significant difference was got(P0.05).The result of visual evaluation was that the scores of the whitening product were higher than those of vehicle with no significant difference(P0.05).Conclusion This study showed that the time-course of pigmentation formation induced by repeated UV exposure persisted about 20 days.The combinations of subjective and objective methods are advised to assess the whitening products.