[Skin damage caused by optical radiation beyond UV]

Along with other environmental factors, ultraviolet radiation (UV-B, UV-A) definitely plays a role in skin aging and skin cancer. Recently, it has been shown that visible light and infrared radiation are also involved in the skin aging process. Visible light in the blue-green spectral range can be absorbed by certain molecules of the skin in a similar way to UV-A, thereby generating reactive oxygen species (ROS). Light in this spectral range can trigger erythema and an increase in pigmentation, possibly also inducing the expression of matrix metalloproteinases (MMP) such as MMP‑1 and, thus, contributing to visible skin aging. In contrast, visible light in the red spectral range can have the opposite effect, reducing erythema and periorbital rhytides (photorejuvenation). Radiation in the near-infrared spectral range (IR-A) penetrates deep into the skin and can increase the temperature in the skin through absorption in water, thereby altering cell activities. IR‑A radiation can be absorbed by biomolecules such as cytochrome c oxidase in the mitochondria of fibroblasts, where it triggers a significant increase in ROS. This results in a retrograde signaling cascade toward the cell nucleus and the expression of many genes, including MMP‑1. Under IR‑A, collagen formation also declines and angiogenesis occurs. All of these effects of IR‑A contribute to skin aging. Protective filters for the skin, such as those used for UVR radiation, are not available for IR and visible light. The use of creams containing antioxidants or iron oxide pigments could offer some protection in these spectral ranges.