Photosensory Function, Reception and Response in Human Skin

Human skin has a photosensory system comprised of several opsins, light-sensitive proteins, and their signalling pathways as peripheral sensors and effectors mainly orchestrated through the melanocyte but also involving keratinocytes, fibroblasts and hair follicle cells. It has been shown that UVA radiation can lead to an Immediate Pigment Darkening (IPD) response in melanocytes. Necessity of a protective response is obvious but this system feeds into a neuronal and hormonally-mediated centralised system of clock-like responses that not only respond to immediate threats but also demonstrating an established mechanism to anticipate changes in the day/night and seasonal cycles that have profound effects on the behaviour of the organism as a whole.