National Institute of Mental Health

Most likely, depression is caused by a combination of genetic, biological, environmental, and psychological factors.

Depressive illnesses are disorders of the brain. Brain-imaging technologies, such as magnetic resonance imaging (MRI), have shown that the brains of people who have depression look different than those of people without depression. The parts of the brain involved in mood, thinking, sleep, appetite, and behavior appear different. But these images do not reveal why the depression has occurred. They also cannot be used to diagnose depression.

Some types of depression tend to run in families. However, depression can occur in people without family histories of depression too. Scientists are studying certain genes that may make some people more prone to depression. Some genetics research indicates that risk for depression results from the influence of several genes acting together with environmental or other factors. In addition, trauma, loss of a loved one, a difficult relationship, or any stressful situation may trigger a depressive episode. Other depressive episodes may occur with or without an obvious trigger.

Signs & Symptoms

“It was really hard to get out of bed in the morning. I just wanted to hide under the covers and not talk to anyone. I didn’t feel much like eating and I lost a lot of weight. Nothing seemed fun anymore. I was tired all the time, and I wasn’t sleeping well at night. But I knew I had to keep going because I’ve got kids and a job. It just felt so impossible, like nothing was going to change or get better.”

People with depressive illnesses do not all experience the same symptoms. The severity, frequency, and duration of symptoms vary depending on the individual and his or her particular illness.

Signs and symptoms include:

• Persistent sad, anxious, or “empty” feelings
• Feelings of hopelessness or pessimism
• Feelings of guilt, worthlessness, or helplessness
• Irritability, restlessness
• Loss of interest in activities or hobbies once pleasurable, including sex
• Fatigue and decreased energy
• Difficulty concentrating, remembering details, and making decisions
• Insomnia, early-morning wakefulness, or excessive sleeping
• Overeating, or appetite loss
• Thoughts of suicide, suicide attempts
• Aches or pains, headaches, cramps, or digestive problems that do not ease even with treatment.