A product of the pineal gland in the brain, melatonin is responsible for regulating the sleep cycle. When it’s functioning at its peak, melatonin production ramps up at night to prepare your body for sleep and it decreases in the morning as you rise and shine. It is now believed that melatonin also helps to promote antioxidants that counter the free radicals that develop in your skin throughout the day in reaction to things like sun exposure and pollution.