Melatonin is a type of hormone secreted by pineal gland, a tiny structure located at the base of the brain which helps regulate other hormones and maintains the body's circadian rhythm. The circadian rhythm is what we normally refer to as our body clock which plays a critical role in determining when we fall asleep and when we wake up. Darkness triggers the production of melatonin while light restrains its activity. Exposure to too much light in the evening or too little light during the day can disrupt the body’s normal melatonin cycles.