UV Photoprotection and Long-lasting Pigmentation from UVA and/or UVB

To test whether there is a photoprotective benefit after different types of suberythemal repetitive UV, a 1.5 MED challenge dose was applied 1 week after the initial 2 weeks of repetitive irradiation.  To determine what different mechanisms and/or factors might be involved in physiological pigmentary responses of the skin to different types of UV, we used whole human genome microarrays and immunohistochemical analyses to characterize human skin in situ to examine how melanocyte-specific proteins and paracrine melanogenic factors are regulated by repetitive exposure to suberythemal doses of different types of UV (UVA and/or UVB). Seven volunteers with skin type II-III were irradiated with UVA, UVB or UVA+UVB radiation for 2 weeks (5 times per week, 10 times total) after preliminary determination of their MEDs. A UVA+UVB challenge dose of 1.5X the MED was applied 1 week later.  Biopsies were taken before the challenge dose, immediately after the challenge dose, 4 days after the challenge, and 15 weeks after the challenge.