Obsessions are intrusive, irrational thoughts—unwanted ideas or impulses that repeatedly appear in a person's mind. Again and again, the person experiences disturbing thoughts, such as "My hands must be contaminated; I need to wash them"; "I may have left the gas stove on; I need to go check it fast"; "I am going to injure my child by accident; I need to be very careful or else something bad will happen." On one level, the person experiencing these thoughts knows their obsessions are irrational. But on another level, he or she fears these thoughts might be true. Trying to avoid such thoughts creates great anxiety, distress and dysfunction.
Compulsions are repetitive rituals such as hand washing, counting, checking, hoarding or arranging. An individual repeats these actions many times throughout the day and performing these actions releases anxiety, but only momentarily. People with OCD feel they must perform these compulsive rituals or something bad will happen to them or their loved ones.
Most people at one time or another experience obsessive thoughts or compulsive behaviors. Obsessive-compulsive disorder occurs when an individual experiences obsessions and compulsions for more than an hour each day, in a way that interferes with his or her life. The National Institute of Mental Health estimates that more than 2 percent of the U.S. population, or nearly one out of every 40 people, will be diagnosed with OCD at some point in their lives. The disorder is two to three times more common than schizophrenia and bipolar disorder.
OCD is often described as "a disease of doubt." Individuals living with OCD experience "pathological doubt" because they are unable to distinguish between what is possible, what is probable and what is unlikely to happen. [ref - NAMI]
Get NAMI's Obsessive Compulsive Disorder Fact Sheet, HERE