Alpha melanocyte stimulating hormone (alpha-MSH) is released from UVR exposed melanocytes and keratinocytes in human skin following exposure to ultraviolet radiation. It is understood to act on the melanocortin-1-receptors (MC1R) to, exclusively in melanocytes, induce synthesis of the brownish-black melanin pigment. MC1R are expressed on keratinocytes as well as number of other cells including, bu