Ultraviolet B (UVB)-irradiated skin pigmentation was quantified using 2 objective and noninvasive techniques. Ten healthy volunteers were exposed to increasing UVB doses in the interval from 6 mJ/cm2 to 120 mJ/cm2 and the resultant vascular and pigmentary changes were evaluated using laser Doppler flowmetry (LDF) and reflectance spectroscopy (RS). Measurements were made 0.25 h, 1 h, 4 h, 8 h, 24 h, 72 h and 192 h post-irradiation. Visual scores were determined 24 h post-irradiation. Both RS and LDF revealed an early and rapid erythematous response to UVB irradiation, peaking between 8 h and 24 h, with no single UVB dose showing any significant increase until 4 h post-irradiation. LDF showed a peak increase in blood flow at 8 h post-irradiation for sites with low UVB exposure (less-than-or-equal-to 36 mJ/cm2). Doses greater-than-or-equal-to 42 mJ/cm2 showed maximal increase at 24 h. After this increase in blood flow, a slow normalization began that was not complete at 192 h post-irradiation at sites exposed to greater-than-or-equal-to 60 mJ/cm2. The present RS analysis is able to distinguish between oxygenized (OH) and deoxygenized hemoglobin (DOH). The only significant increase in DOH was found for the averaged 6 mJ/cm2 and 12 mJ/cm2 UVB dose sites 24 h after irradiation. OH peaked 24 h post-irradiation and resolution was still incomplete after 192 h. RS revealed no dose, as did the LDF, below which the vascular response peaked earlier. LDF measures dermal blood flow and RS measures hemoglobin content in the skin. These technical differences may explain the different peak and resolution dynamics of UVB-induced erythema measured by the 2 techniques. This study showed that the sensitivity of the 3 methods varied with post-irradiation time. At 1 h, 4 h and 8 h after irradiation, LDF was more sensitive then RS, but from 24 h and until 192 h RS was more sensitive. At 24 h after UVB irradiation, the sensitivity of the 3 techniques was: RS > LDF > visual score.
