The exact cause of depression isn't known. A person's genetics, the balance of chemicals in the brain, or the environment he or she lives in may be involved. There also appears to be a psychological element to depression.
It is most likely, however, that depression isn't "caused" by any one thing. Instead, it is the end result of a combination of influences.
Let's take a closer look at how each of these factors may contribute to depression.
Depression appears to run in families, which suggests that genetics play a part in a person developing the condition. If you have a family member who has suffered from depression, you may be more likely to develop it, but there is no guarantee. This increased likelihood of developing depression is often referred to as a "genetic predisposition."
You might have also heard that depression is caused by an imbalance of certain chemicals in the brain called neurotransmitters. These neurotransmitters allow brain cells to communicate with each other by sending and receiving messages.
These are the same chemicals that many of the current depression medications affect. Since these medicines are useful in treating depression, it can be assumed that neurotransmitters have an impact on depression. What is not known is whether a chemical imbalance plays a part in causing depression or if the imbalance occurs as the result of a person being depressed.
Environmental factors also appear to play a role in a person developing depression. A loss of a loved one, chronic illness, stress at work or home, or unwelcome life changes can often trigger a depressive episode, even in individuals without a family history.
Finally, psychological factors may influence a person's chances for developing depression. This includes such things as poor coping skills, negative thinking, and judgment problems.
There is no simple answer as to what causes depression. But it may help to think about these different factors and how they interact as blocks. Some of these "blocks" may be tall, some short. They may stay the same height during a lifetime or change with time. And because each person is different, these blocks can vary in size based on the degree of influence that each factor has on an individual.
Now stack all of the blocks.
For each individual, there is some critical level, or threshold, that determines if a person will develop depression. If the total combined height of an individual's "blocks" is below this threshold, a person will often function normally. Above this level, a person will develop depression.
REMEMBER: These factors can change with time.
Take two people -- one with a tall block because of his or her genetics and one with a small block. Now add all the other "block" influences. If an environmental stress, like losing a job, occurs, this could push the genetically predisposed person over his or her threshold. This same stress might not affect the other person because the combined height of his or her blocks is relatively small.
This does not mean, however, that the other individual can't experience depression. This person could experience another stress, such as the death of a loved one, that pushes him or her over the threshold.