A hormonal substance that can lighten the color of skin pigments. This hormone is synthesized in the pineal gland using tryptophan as the matrix, and its chemical name is N-acetyl and 5-methoxytryptamine.

Melatonin is the earliest biologically active substance found in the pineal gland. When mammals are in the dark, melatonin secretion activity is strengthened immediately; when it is transferred to a bright environment, it stops secretion. The rhythm of melatonin secretion can be measured from the urine as the light changes. Other factors such as sleep, diet, mental state, and stress also have certain effects. Injecting melatonin into the hypothalamus can inhibit the secretion of gonadotropins, but it was also observed that melatonin can directly act on the pituitary. Therefore, melatonin can inhibit the secretion of gonadotropin through the hypothalamus and / or pituitary. In addition, melatonin receptors have also been found in the ovary, indicating that this is also the site of action of melatonin