Rise in use of 'dangerous' tanning injection Channel 4 News Your body already makes a hormone that tells your skin to tan. Melanotan 2 is a synthetic peptide engineered to mimic that hormone but in a version that's more potent and longer lasting than Red hair comes with a hidden biological advantage. Scientists have discovered that pheomelanin, the pigment responsible for red hair and fair skin in humans, as well as orange feathers in birds, may Melanocortin 1 receptor gene