Photoaging is a common skin condition characterized by wrinkles, dyspigmentation and sagging skin. It is caused by chronic exposure to UVA (320-400nm) and UVB (280-320nm). UVA is more abundant in sunlight than UVB and penetrates deeper into the dermis and considered to be the major culprit of photoaging. Previous research done on lighter skin types established upregulation collagen breakdown by matrix metalloproteinases (MMP) with concurrent reduction in procollagen synthesis as surrogate markers for wrinkled skin. Photoaging is less severe clinically in darker skin types but not absent. This study examines the effects of low level UVA1 (340-400nm) irradiation on expression of MMPs and procollagen in darker skin types (Fitzpatrick Skin Types [FST] V and VI). 12 subjects with FST V and VI were randomized to receive 20 J/cm2 of UVA1 on the buttocks as a single or repetitive exposure. Group 1 (n=6) received one exposure, and skin biopsies were done at 1 hour-, 24 hours-, and 7 days- post exposure. Group 2 (n=6) received 3 consecutive daily exposures, and biopsies were done 24 hours after each exposure. Quantitative RT-PCR measured the expression of MMP-1, MMP-3, procollagen 1 and 3. Gene expression from the irradiated skin was compared to non-irradiated buttock skin. Skin pigmentation was measured by a colorimeter before and after each exposure. For group 1, there was significant skin darkening 1 hour after a single exposure, and no significant change was noted in MMP (1,3) and procollagen (1,3) expression at all time points. However, for group 2, after 3 consecutive exposures to low level UVA1, skin darkened significantly after each exposure, and there was a significant increase in MMP-3 expression (p=0.019) but not in MMP-1 and procollagen (1,3). Our data show that repetitive exposures to low level UVA1 irradiation induces MMP-3 expression in darker skin types, suggesting that pigmented skin types are still susceptible to UV-induced collagen breakdown.  This preliminary evidence reiterates the importance of photoprotection in darker skin types.

The molecular effects of low dose (20 J/cm2) UVA1 on darker skin types of human