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

Background: Compared 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. Objectives: To 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. Methods: The buttocks of 16 healthy volunteers (aged 24-43 years, 10 mate 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 atone, the exposed sites were covered with either a UV fitter or black cloth, respectively, during irradiation. Skin samples were taken 24 h later. Results: IR/visible tight 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, white UV, IR/visible tight and heat contributed to macrophage infiltration. Conclusions: IR/visible light and heat of natural sunlight, in addition to UV, play a rote in modulating the expressions of MMPs and procollagen, and inflammatory cell infiltration in human skin. (C) 2007 Japanese Society for Investigative Dermatology. Published by Elsevier Ireland Ltd. All rights reserved.