UV transmission and UV protection factor (UPF) measured on split skin following exposure to UVB radiation - correlation with the minimal erythema dose (MED)

In this study the ultraviolet (UV) transmission of split skin exposed to WB radiation and of non-exposed skin was compared in the 280-390 nm wavelengt h range and quantified. In addition, the correlation between the increase i n the minimal erythema dose (MED) associated with a defined exposure to UVB and the ultraviolet protection factor (UPF) calculated from the transmissi on data was investigated. The study population consisted of 12 patients. Tw o pieces of split skin of the same thickness (0.3 mm) were taken from the r ight thigh of each patient. One specimen was removed from an area of non-ex posed healthy skin and the other from an area which had been exposed to UVB radiation for a period of 12 days in which the initial dose of 1/3 MED was raised by 1/3 MED every 4 days. The split skin specimens were stretched ov er a special frame; subsequently, the UV transmission was determined with a spectrophotometer. The mean values obtained for UV transmission were all s ignificantly below the initial data for non-exposed split skin. In the UV r ange of 280-390 nm, the transmission measured in the exposed specimens was 49.1% of the value measured in the non-exposed split skin (P<0.05). The cor responding values for the WA range (315-390 nm) and the UVB range (280-315 nm) were 50.1% and 29.5%, respectively (P<0.05), based on the initial trans mission data obtained from non-exposed skin. The clinical determination of MED after 12 days of exposure to UVB yielded mean values that were 3.2 time s the initial values. Moreover, the mean UPFs calculated from the transmiss ion data measured at the end of the 12-day exposure period were also about three times the initial values. The present study has thus established a si gnificant correlation between the clinical MED values and the UPFs calculat ed from the transmission data measured following exposure to UVB.