The cause of major depressive disorder is a combination of brain chemistry, family history, and psychosocial environment. Other physiological changes that accompany depression may result in irregular hormone levels in the brain. There is, however, little evidence to support the idea that abnormal hormone levels cause depression. While depression can strike anyone at any time, people suffering from depression may suffer from different types of depression and even display different signs and symptoms depending on the gender, age, and ethnic and cultural groups.

Research has identified several factors associated with an increased risk for depression which are as follows:

Family History: Having an immediate family member with depression increases the risk of developing depression. Studies report that depression for even 1 - 2 months in a mother increases the risk for depression in her children. In such cases, genetic or environmental factors or both may be responsible. Other mental illnesses, such as alcoholism in family members, can also increase the risk for depression. Spouses of partners with depression are themselves at higher risk for depression.

Medications: A number of drugs taken for chronic problems cause depression. Among them are pain relievers for arthritis, cholesterol-lowering drugs, medications for high blood pressure and heart problems, and bronchodilators used for asthma and other lung disorders.

Gender: It is estimated that one out of every four women and one out of every 10 men experience some type of depression during their lifetime. While women suffer from depression more often and attempt suicide more frequently, men are more successful in their suicide attempts. Women also suffer from unique forms of depression related to their unique biology and life experiences.

Age: Most people experience their first episode of depression between the ages of 20 and 40. In fact, the average age of onset for depression is the mid-20s. Alarmingly, recent research shows that the average age of onset is decreasing with each generation. Children, adolescents and elderly persons often display unique symptoms of depression and have specific stressful events that predispose them to depression.

Insomnia and Sleep Disorders: Sleep abnormalities are an integral part of depressive disorders, with more than 90% of depressed patients experiencing insomnia. Although stress and depression are major causes of insomnia, insomnia may also increase the activity of the hormones and pathways in the brain that can produce emotional problems.