The pineal gland, also called epiphysis, is a gland that secretes hormones that control the body’s biological clock since it regulates the sleep-wake cycle (circadian rhythm). It is located in the central part of the brain and since ancient times it has been recognised as the gland that perceives the environment. When light decreases, the pineal gland is responsible for producing melatonin, a neurotransmitter that induces sleep. Furthermore, melatonin is also an antioxidant and powerful regulator of stress as it plays a role in cell regeneration. Therefore, its production is often related to the apathy and the blues that people experience during autumn and winter, opposed to the high levels of energy that the sunny days cause.