MMP9 and rosacea: UV radiation is known to damage superficial cutaneous vasculature and the elastic and collagen fibres that comprise the dermal matrix.31 UV radiation also results in the upregulation of MMPs involved in collagenolysis, inflammation, and angiogenesis.44 In particular, MMP9 has been found to be upregulated in rosacea patients.17 MMP9 activity leads to the release of pro-inflammatory cytokines including IL-8, which inhibits the production of collagen and further activate MMP9, creating a chronic inflammatory cycle.45