Melatonin is a hormone secreted by the pineal gland which is responsible for the lightning of the skin. Melatonin is the hormone responsible for sleeping and waking cycles. People who are suffering from chronic insomnia usually use melatonin supplements, however it is not recommended for all patients with sleep problems. In vertebrates this hormone is derived from serotonin, this is responsible for darkness of the skin. Melatonin journals deals with penial gland secreations.