Infrared plus visible light and heat from natural sunlight participate in the expression of MMPs and type I procollagen as well as infiltration of inflammatory cell in human skin in vivo

SummaryBackgroundCompared with the detailed characterization of the ultraviolet (UV) response in human skin, the effects of infrared (IR) and other regions of the sunlight are scarce.ObjectivesTo determine the participation of IR/visible light and heat components of the sunlight on matrix metalloproteinases (MMPs) and type I procollagen expression, and inflammatory cell infiltration in human skin in vivo.MethodsThe buttocks of 16 healthy volunteers (aged 24–43 years, 10 male and 6 female) were irradiated with a 1.1–3 minimal erythema dose (MED) of natural sunlight. To determine the differential effects of UV, IR/visible rays and solar heat alone, the exposed sites were covered with either a UV filter or black cloth, respectively, during irradiation. Skin samples were taken 24 h later.ResultsIR/visible light spectrum of sunlight significantly increased MMP-1 and MMP-9 expression and decreased type I procollagen expression. Solar heat also contributed to the increased MMP-1 expression. Only the UV region recruited neutrophils into the dermis, while UV, IR/visible light and heat contributed to macrophage infiltration.ConclusionsIR/visible light and heat of natural sunlight, in addition to UV, play a role in modulating the expressions of MMPs and procollagen, and inflammatory cell infiltration in human skin.