Persistent depressive disorder symptoms usually come and go over a period of years, and their intensity can change over time. But typically symptoms don't disappear for more than two months at a time. In addition, major depression episodes may occur before or during persistent depressive disorder — this is sometimes called double depression.

Symptoms of persistent depressive disorder can cause significant impairment and may include:

• Loss of interest in daily activities
• Sadness, emptiness or feeling down
• Hopelessness
• Tiredness and lack of energy
• Low self-esteem, self-criticism or feeling incapable
• Trouble concentrating and trouble making decisions
• Irritability or excessive anger
• Decreased activity, effectiveness and productivity
• Avoidance of social activities
• Feelings of guilt and worries over the past
• Poor appetite or overeating
• Sleep problems

In children, symptoms of persistent depressive disorder may include depressed mood and irritability.

The exact cause of persistent depressive disorder isn't known. As with major depression, it may involve more than one cause, such as:

• Biological differences. People with persistent depressive disorder may have physical changes in their brains. The significance of these changes is still uncertain, but they may eventually help pinpoint causes.
• Brain chemistry. Neurotransmitters are naturally occurring brain chemicals that likely play a role in depression. Recent research indicates that changes in the function and effect of these neurotransmitters and how they interact with neurocircuits involved in maintaining mood stability may play a significant role in depression and its treatment.
• Inherited traits. Persistent depressive disorder appears to be more common in people whose blood relatives also have the condition. Researchers are trying to find genes that may be involved in causing depression.
• Life events. As with major depression, traumatic events such as the loss of a loved one, financial problems or a high level of stress can trigger persistent depressive disorder in some people

Persistent depressive disorder often begins early — in childhood, the teen years or young adult life — and is chronic. Certain factors appear to increase the risk of developing or triggering persistent depressive disorder, including:

• Having a first-degree relative with major depressive disorder or other depressive disorders
• Traumatic or stressful life events, such as the loss of a loved one or financial problems
• Personality traits that include negativity, such as low self-esteem and being too dependent, self-critical or pessimistic
• History of other mental health disorders, such as a personality disorder

Conditions that may be linked with persistent depressive disorder include:

• Reduced quality of life
• Major depression, anxiety disorders and other mood disorders
• Substance abuse
• Relationship difficulties and family conflicts
• School and work problems and decreased productivity
• Chronic pain and general medical illnesses
• Suicidal thoughts or behavior
• Personality disorders or other mental health disorders