Causes of Depression The sources of depression are complex. Genetic, biological, and environmental elements can contribute to its development. In some people, depression could be traced to a single trigger, while in others, a number of causes are in play always in trouble . For many, the causes are never known. Currently, it appears that there are biochemical causes for unhappiness, occurring due to abnormalities in the degrees of certain chemicals in the brain. These chemicals are called neurotransmitters. The abnormalities are usually biological and are not caused by anything you did. While we still have no idea exactly how levels of these neurotransmitters influence mood, we can say for certain that the levels can be affected by numerous factors.