Health A-Z

Medical Content Created by the Faculty of the
Harvard Medical School

Obsessive-Compulsive Disorder (OCD)

What Is It?

In obsessive-compulsive disorder (OCD), a person is troubled by intrusive, distressing thoughts (obsessions) and feels the pressure to carry out repetitive behaviors (compulsions).

The exact cause of OCD remains a mystery. Neuroscientists believe that the brain pathways involved with judgment, planning and body movement are altered in this illness. Environmental influences, such as family relationships or stressful events, can trigger or worsen OCD symptoms.

OCD affects an estimated 2% to 3% of people in the United States. The percentage is about the same in Canada, Korea, New Zealand and parts of Europe. About two-thirds of people with OCD have the first symptoms before they are 25 years old. Only 15% develop their first symptoms after age 35. There is strong evidence that the illness has a genetic (inherited) basis, since about 35% of people with OCD have a close relative who also has the condition. Although 50% to 70% of patients first develop OCD after a stressful life event – such as a pregnancy, a job loss or a death in the family – experts still do not understand exactly how stress triggers the symptoms of this illness.

Sometimes people with OCD manage their obsessions without giving any external sign that they are suffering. Usually, however, they try to relieve their obsessions by performing some type of compulsion: a repeated ritual that is aimed at soothing their fears. For example, a woman who has the obsession that her hands are dirty may develop the compulsion to wash them 50 times a day. A man who fears that his front door is unlocked may feel compelled to check the lock 10 or 20 times each night.