Life is full of changes. Everyday events and our reactions to them sometimes interfere with our sense of well-being and peace of mind. It is common to get the blues or become sad when disappointed. Symptoms of depression are the most common medical problems seen by health professionals. It is estimated that feelings of depression will affect about one-third of all adults in the United States at some time in their lives.

Most people experience feelings of sadness over such losses as divorce or separation, the death of a friend or loved one, or a job change or layoff. These feelings are an expected reaction to a "triggering event," and most people get over them in time.

Several factors increase your risk of developing feelings of depression, such as:

• Female sex. Women are twice as likely as men to experience feelings of depression. Hormonal changes may play a role in these feelings, which may be more evident during pregnancy, especially shortly after the birth of a baby (postpartum depression) or shortly before or during menopause. Some women experience feelings of sadness or depression shortly before the start of menstruation (premenstrual syndrome, or PMS).
• Age older than 60. Feelings of depression in this age group are frequently overlooked because the symptoms are similar to other diseases and problems experienced by older adults. Adults in this age group are more likely to experience social isolation. Feelings of sadness may accompany other life events, such as retirement, death of a spouse or child, or declining physical abilities.
• Personal or family history. You are more likely to experience feelings of depression if you have a history of previous depression, an anxiety disorder, or another mental illness. You are also 2 to 3 times more likely to experience feelings of depression if one or both of your parents were diagnosed with depression.
• Medical problems-such as cancer, kidney disease, heart disease, or Parkinson's disease-or alcohol or substance abuse or withdrawal.
• Stressful life events, such as changing jobs, the loss of a job, or children leaving home.
• Lack of family or social support.
• Having less than a high school education.

Symptoms of depression that may indicate a need for treatment vary from person to person. If you experience feelings of sadness or loss of interest in pleasurable activities plus 4 or more of the following symptoms for 2 weeks or longer, you may be depressed.

• Changes in appetite or weight
• Restlessness or decreased activity that is noticed by others
• Feeling tired or sleepy all of the time
• Trouble sleeping or sleeping more than usual
• Inability to concentrate or make decisions
• Feelings of hopelessness
• Feelings of worthlessness or guilt
• Preoccupation with death or recurrent thoughts of suicide

Because "mood swings" and other emotional changes are considered a normal part of growing up, depression in children and teens often goes unrecognized. Children and teens do develop depression, and it can affect a child's quality of life. If prolonged or severe depression is left untreated, it can lead to serious outcomes, including suicide attempts and even completed suicide.

Depression is the most important risk factor for suicide. For more information, see the topic Depression.

Review the Emergencies and Check Your Symptoms sections to determine if and when you need to see a health professional.