The (MC1R), also known as MSHR) is a G protein-coupled receptor which binds to a class of pituitary peptide hormones known as the melanocortins, of which include adrenocorticotropic hormone (ACTH) and the different forms of melanocyte-stimulating hormone (MSH). MC1R is one of the key proteins involved in regulating mammalian skin and hair color. It is located on the plasma membrane of specialized cells known as melanocytes, which produce the pigment melanin through a process referred to as melanogenesis. It works by controlling the type of melanin being produced and its activation causes the melanocyte to switch from generating the yellow or red phaeomelanin by default to the brown or black eumelanin in replacement.