What Are the Causes of Clinical Depression?
Many things can contribute to clinical depression. For some people, a number of factors seem to be involved, while for others a single factor can cause the illness. Oftentimes, people become depressed for no apparent reason.
Biological - People with depression may have too little or too much of certain brain chemicals, called "neurotransmitters." Changes in these brain chemicals may cause or contribute to depression.
Cognitive - People with negative thinking patterns and low self-esteem are more likely to develop clinical depression.
Gender - More women experience depression than men. While the reasons for this are still unclear, they may include the hormonal changes women go through during menstruation, pregnancy, childbirth and menopause. Other reasons may include the stress caused by the multiple responsibilities that women have.
Co-occurrence - Depression is more likely to occur along with certain illnesses, such as heart disease, cancer, Parkinson's disease, diabetes, Alzheimer's disease, Multiple Sclerosis and hormonal disorders.
Medications - Side effects of some medications can bring about depression.
Genetic - A family history of depression increases the risk for developing the illness. Some studies also suggest that a combination of genes and environmental factors work together to increase risk for depression. 
Situational Difficult life events, including divorce, financial problems or the death of a loved one can contribute to depression.
What Are the Different Kinds of Depression?
Depressive Disorders are a category of mood disorders that involve extended periods of feeling extremely low and disrupt a person’s ability to enjoy life. Some of the most common Depressive Disorders include:
Major Depressive Disorder (Clinical Depression); a mental health condition characterized by an inescapable and ongoing low mood often accompanied by low self-esteem and loss of interest or pleasure in activities that a person used to find enjoyable. To meet the criteria for
Major Depressive Disorder (MDD), symptoms must be present nearly every day for at least 2 weeks. MDD is also often referred to as Major Depression.
Persistent Depressive Disorder; refers to a longer lasting form of depression. While Major Depressive Disorder is diagnosed if an individual experiences symptoms for at least 2 weeks, Persistent Depressive Disorder is used when symptoms of depression are present on most days for at least two years, but do not reach the severity of a major depressive episode. (Prior to the release of the DSM-5 this was more commonly known as Dysthymia.)
Post-Partum Depression; depression that starts after child birth and lasts at least two weeks, up to a year.
Premenstrual Dysphoric Disorder; a severe form of Pre-Menstrual Syndrome that is diagnosed when a woman experiences severe symptoms of depression, tension, and irritability in the week prior to menstruation. While it isn’t uncommon for most women to experience emotional and physical changes prior to menstruation, women who meet criteria for PMDD experience changes that impact their lives in more profound ways.
Seasonal Affective Disorder; a mood disorder involving symptoms of depression associated with varying levels of sunlight during fall and winter months which subsides during spring and summer.
Depression is also a feature of Bipolar Disorder.
What Are the Symptoms of Clinical Depression?
What Are the Treatments for Depression?
Depression is very treatable, with the overwhelming majority of those who seek treatment showing improvement.
The most commonly used treatments are antidepressant medication, psychotherapy or a combination of the two.
Learn more about therapy and medication.
The choice of treatment depends on the pattern, severity, persistence of depressive symptoms and the history of the illness. As with many illnesses, early treatment is more effective and helps prevent the likelihood of serious recurrences. Depression must be treated by a physician or qualified mental health professional.
For some people, depression can be very stubborn to treat and may require additional treatment options.
Content source from: http://www.mentalhealthamerica.net/conditions/depression