Souce: Synthesis.

Variations in skin colour are caused by different levels of melanin in the skin. Regular exposure to the sun causes brown spots known as sunspots and their occurrence increases with age. Classic descriptions of these troubles refer to hyperactivity of the melanocytes, which synthesize abnormal amounts of melanin.

Alpha Melanocyte Stimulating Hormone also named Melanotropin (a-MSH) is the natural substance produced by our body which is responsible for several physiological activities like pigmentation.

Tyrosinase is stimulated by the bonding of a-MSH on its specific receptor MC1-R. The stimulation of the tyrosinase activity, induces the hydroxylation of the amino acid tyrosine to DOPA (dihydroxyphenylalanine) and catalyses its oxidation to dopaquinone. The final step is the synthesis of melanin in organelles called melanosomes, in melanocytes.
The ideal skin lightening agent for cosmetic products is one that inhibits melanogenesis without cytotoxicity.

Mechanism of action
Binding of a-MSH to the MC1-Receptor on melanocytes is the first step in melanogenesis and the pigment formation. By binding and blocking the MC1-R, we can block the intracellular melanogenesis pathway and decrease the synthesis or the over expression of melanin produced by melanocytes.

Nonapeptide-1 an oligopeptide with an high affinity for MC1-R. It is a biomimetic peptide antagonist specific of the a-MSH (Alpha Melanocyte Stimulating Hormone). As an antagonist, it competes against the natural ligand (a-MSH) on its specific receptor (MC1-R) by preventing any further activation of the tyrosinase, and thus blocking melanin synthesis. Tyrosinase inhibition reduces the formation of unwanted pigmentation allowing for the control over skin tone and brown spots.

Nonapeptide-1 blocks the melanogenesis pathway and inhibits tyrosinase activity and melanin synthesis.