Depression, in everyday language, refers to any downturn in mood, which may be relatively transitory and perhaps due to something trivial. This is differentiated from Clinical depression which is marked by symptoms that last two weeks or more and are so severe that they interfere with daily living.

In the field of psychiatry the word depression can also have this meaning but more specifically refers to a mental illness when it has reached a severity and duration to warrant a diagnosis. The Diagnostic and Statistical Manual of Mental Disorders (DSM) states that a depressed mood is often reported as being: "... depressed, sad, hopeless, discouraged, or 'down in the dumps'."

In a clinical setting, a depressed mood can be something a patient reports (a symptom), or something a clinician observes (a sign), or both.

Determinants of mood:

Depression can be the result of many factors, individually and acting in concert.


Reactions to events, often a loss in some form, are perhaps the most obvious causes. This loss may be obvious, such as the death of a loved one, or having moved from one house to another (mainly with children), or less obvious, such as disillusionment about one's career prospects. Monotonous environments can be depressing. The mere fact of painting a workplace can stimulate productivity. A lack of control of one's environment can lead to feeling of helplessness. Domestic disputes and financial difficulties are common causes of a depressed mood.

Internal psychological factors:

Sometimes the depressed mood may relate more to internal processes or even be triggered by them. Pessimistic views of life or a lack of self-esteem can lead to depression. Illnesses and changes in cognition that occur in psychoses and dementias, to name but two, can lead to depression.

Biological models of causation:

These are varied but generally include hereditary, neurotransmitter, hormonal, illness and seasonal factors which are more fully discussed in the clinical depression article.

Adaptive benefits of depression:

While a depressed mood is usually seen as deleterious, it may have adaptive benefits. Of interest is the fact that physical illness tends to lead to depressive behaviour and some diseases, such as influenza, are often accompanied by a degree of depression that seems out of proportion to the physical illness. A depressed mood is adaptive in illness in that it leads to the person resting and in general elicits care. Seasonal affective disorder may point to an atavistic link with behaviour in hibernation.

Mental disorders with depression:

A depressed mood is usually a core feature of some mental disorders such as:

  1. Manic depression (Bipolar disorder)
  2. Clinical depression
  3. Endogenous depression
  4. Reactive or neurotic depression
  5. Atypical depression
  6. Psychotic depression
  7. Seasonal affective disorder
  8. Adjustment disorder with depressed mood