Melatonin (also known as melatonin, melatonin, melanin inhibition and pineal hormone) is an amine hormone produced by the pineal gland of mammals and humans, which can make a cell producing melanin glow, hence the name melatonin. It exists in many organisms, from algae to humans, and its content level changes with the time of day.

A hormone substance that can lighten the color of skin pigment. This hormone is synthesized in the pineal gland based on tryptophan, and its chemical name is N- acetyl, 5- methoxytryptamine.

Melatonin is the first bioactive substance found in the pineal gland. When mammals are in the dark, the secretion of melatonin will be enhanced immediately. Secretion stops when turning to bright environment. The rhythm of melatonin secretion can be measured from urine with the change of light.

Injection of melatonin into hypothalamus can inhibit the secretion of gonadotropin, but it is also observed that melatonin can directly act on pituitary gland. Therefore, melatonin can inhibit gonadotropin secretion through hypothalamus and pituitary gland. In addition, melatonin receptor was also found in the ovary, which indicates that this is also the site of melatonin action.