[Photoaging and infrared radiation. Novel aspects of molecular mechanisms].

Human skin is exposed to infrared (IR) radiation (760 nm-1 mm) from natural and artificial sources. In particular, the use of IR for cosmetic and "wellness" purposes has become increasingly popular and viewed as completely safe. However, epidemiological data and clinical observations indicate that IR radiation cannot be considered as totally innocuous to human skin. In particular, IR radiation, just as UV radiation, seems to be involved in photoaging and potentially also in photocarcinogenesis. In recent studies the molecular mechanisms involved in this process such as cellular signal transduction and gene expression have been characterised. IR radiation induces the synthesis of matrix metalloproteinase-1 via the mitogen-activated protein kinase signalling pathway. Since this mechanism is a major pathophysiologic factor in UV-induced skin ageing, its activation by IR radiation points to a role of IR in premature skin ageing and indicates the potential need for protection against unwanted IR effects.