Melanotan 1 and 2 are peptides that stimulate melanin production in the skin, causing tanning without sun exposure. They work by activating melanocortin receptors on melanocytes, the skin cells that produce melanin pigment in response to UV radiation. This allows the peptides to induce tanning through increased melanin rather than through sun exposure. The peptides are popular among those seeking a tan but are also being studied to help conditions where people are sensitive to UV rays. Users report tanning in areas not usually exposed to the sun.