Melanin-concentrating hormone (MCH) is a cyclic orexinogenic hypothalamic peptide originally isolated from the pituitary gland of teleost fish where it controls skin pigmentation.  In mammals it is involved in the regulation of feeding behavior and energy balance. When administered artificially, it increases food intake. It also seems to activate the stress axis.

Two Melanin concentrating hormone receptors have recently been characterized: MCH-R1 and MCH-R2. These two receptors share approximately 38% homology. MCH-R1 is expressed in all mammals.  MCH-R2 is only found in some primates and carnivores including dogs, ferrets and man.

In humans, melanin is found in skin, hair, the pigmented tissue underlying the iris, the medulla and zona reticularis of the adrenal gland, the stria vascularis of the inner ear, and in pigment bearing neurons of certain deep brain nuclei such as the locus ceruleus and the substantia nigra. Melanin is the primary determinant of human skin color. Dermal melanin is produced by melanocytes, which are found in the stratum basale of the epidermis. Although human beings generally possess a similar concentration of melanocytes in their skin, the melanocytes in some individuals and ethnic groups more frequently or less frequently express the melanin-producing genes, thereby conferring a greater or lesser concentration of skin melanin. Some individual animals and humans have very little or no melanin in their bodies, a condition known as albinism.