Numerous factors can cause depression. Genetics may play a role, for example, in the onset of depression, as can hormones, traumatic events, and even reduced exposure to sunlight. Although not an all-inclusive list, the common causes of depression include some of the following issues. 

Genetics

Your genetics may make you more likely to over or under-produce the brain chemicals implicated in depression. If your parents or siblings tend to experience depression, you're more likely to do so as well. 

Even having extended family members -- like aunts or uncles -- with a history of depression can indicate a genetic component. Researchers have not yet pinpointed the exact genes that cause depression. 

Imbalanced Brain Chemistry

Depression can not only result from an imbalance of chemicals in the brain, but it can also lead to this imbalance after being triggered by another factor, like a traumatic event. The main chemicals -- or neurotransmitters -- responsible for mood regulation are dopamine, serotonin, and norepinephrine. Sometimes the brain doesn't produce these chemicals in sufficient quantities. Other times, there's an adequate supply of these neurotransmitters, but the brain's neurons simply aren't reacting to them appropriately.

Each neurotransmitter also plays a role in other bodily functions, like sleep or digestion. Your specific depression symptoms can help a behavioral health professional pinpoint the chemical that's causing your depression. 

Hormonal Causes

Like neurotransmitters, hormones send necessary signals to the brain. When hormone levels become imbalanced, depression can result. In particular, levels of the hormone estrogen correlate with levels of serotonin. When estrogen production decreases, so will serotonin. 

Excessive or chronically low estrogen can cause depression, especially in women who have just given birth (postpartum depression). Cycles of depression that correlate with a woman's menstrual cycle may point to a condition called a premenstrual dysphoric disorder.

Traumatic Events

Trauma can alter the structure of the brain and reduce its ability to regulate moods and emotions. In turn, that can lead to symptoms of depression. 

Traumatic events can occur in childhood and affect an individual later in life, or the depression may begin immediately after the trauma. Either way, the brain is capable of adapting to its environment. That's great news for depression and trauma recovery because it means the brain can also adapt to a healthier state.

Environmental Factors

Seasonal Affective Disorder, or SAD, is characterized by a bout of depression that occurs each year during the winter months and dissipates on its own once the days get longer. It's believed that exposure to natural sunlight promotes healthy mood regulation in the brain, although the exact mechanism is still under study. When days get shorter and darker in winter, depression can occur. Light therapy may help dissipate those feelings for some.

Understanding what causes depression can be the first step in treatment for it and feeling better.