Our brain is constantly juggling with different thoughts and ideas. There are some automatic behaviors which we repeat frequently without even thinking, for example washing our hands before eating.
However, some people live with invasive ideas or thoughts, that can be persistent, unwanted and sometimes on exaggerated scale. These ideas or thoughts can take up too much space and cause anxiety and even distress. This is called obsessions. To ease the anxiety caused by the obsessive thoughts, that person may feel impelled to mechanically repeat behaviors or do rituals. This is called compulsions. People with obsessive-compulsive disorder or OCD, have either obsessions, compulsions, or both, that potentially affects their normal functioning. People suffering from such a disorder are aware of the irrational and excessive nature of their thoughts and behavior, but they are often unable to drive them out of their minds and control them.
It is estimated that 2-3% of the North American population will suffer from OCD during his life. The diagnosis is made by mental health experts as a host of specific criteria. It is interesting that current treatments can significantly limit the distress of people with OCD and lessen the negative impacts on various aspects of their lives.