This document discusses obsessive-compulsive disorder (OCD), including its causes, symptoms, and treatment. It notes that OCD is characterized by intrusive thoughts that produce anxiety and repetitive behaviors aimed at reducing anxiety. Common OCD symptoms include contamination fears, harm obsessions, and checking, cleaning, and ordering compulsions. The causes of OCD are unclear but may involve biological factors like changes in brain chemistry or genetics as well as environmental influences. Treatment typically involves behavioral therapy and sometimes medication.