Obsessions are recurrent and persistent thoughts, impulses, or images that are intrusive, inappropriate, and cause significant amounts of anxiety or distress. These obsessions are not excessive worries about real-life problems and the person suffering from them realizes that they are irrational and products of his/her own mind. A person suffering from obsessions tries their best to ignore them or to neutralize them with some other thought or action. Common obsessions include thoughts about contamination, repeated doubts, a need to have things in a particular order, aggressive or scary impulses, and sexual imagery.

Compulsions are defined by rigidly applied repetitive behaviors or mental acts that a person feels a need to perform in response to an obsession. The purpose of compulsions is to prevent or reduce distress or prevent some feared event or situation. Further, these behaviors or mental acts are excessive and not realistically connected to what they are supposed to neutralize or prevent. Common compulsions include hand washing, ordering, checking, praying, counting, and repeating words silently.

Obsessive-compulsive disorder is characterized by recurrent and severe obsessions and/or compulsions that are time consuming (i.e., more than one hour per day) or cause large amounts of distress or impairment.

	Examples of Obsessions & Compulsions Example #1 Jack is a 16-year-old high school junior who often experiences intrusive thoughts over and over again about all sorts of scary things. Throughout each day, he worries about such things as catching a disease from touching germs or whether he has locked the door to his house or car. Jack's thoughts are very scary to him and he usually responds by performing various behaviors. For example, in order to reduce his worry about catching a disease, Jack repeatedly washes his hands throughout the day. He always carries around a small bottle of hand-soap and immediately washes his hands in scalding hot water after touching something that could have infected him with germs. Jack spends approximately 90 minutes a day washing his hands. In addition, he attempts to reduce worry about whether he locked the door to his house by checking and rechecking the door 22 times before leaving for school. Further, Jack continues to worry about the door to his house throughout the day and, while at school, counts from 1 to 22 in his head. Although these mental activities seem to help reduce his worry, they significantly impair his ability to pay attention in class. Example #2 Jane is an 8-year-old third grader who has thoughts over and over again about pushing her classmates over the railing from her second floor classroom. These thoughts are very frightening to her and cause her to experience extreme amounts of anxiety and guilt. No matter how hard Jane tries to stop these thoughts, she just cannot seem to control them. The only thing that seems to help lower her levels of worry in response to these intrusive thoughts is for her to silently repeat a prayer to God over and over again. Jane is worried that God will punish her by sending her to Hell for thinking about hurting others and she prays to him every time she gets a scary thought. Jane must say her prayer perfectly or else she feels God will get angry and punish her. These thoughts and prayers cause Jane to worry very much and she is deathly afraid of even hanging out by the railing because she is afraid of pushing someone over the edge.

Source: Barrett, P. M., Farrell, L., Pina, A. A., Piacentini, J., & Peris, T. S. (2008). Evidence-based psychosocial treatments for child and adolescent Obsessive-Compulsive Disorder. Journal of Clinical Child & Adolescent Psychology, 37, 131-155.