Intrusive thoughts about contamination produce intense anxiety that is temporarily relieved only by elaborate washing rituals. Obsessive-compulsive disorder, or OCD, is defined by unwanted, intrusive thoughts (obsessions) and repetitive behaviors or mental acts (compulsions) performed to reduce distress.

Common themes include contamination, harm, symmetry, and forbidden thoughts. The person usually recognizes the thoughts as excessive yet cannot dismiss them. Avoidance and rituals consume time and impair functioning. Neurobiological research points to cortico-striatal circuits; genetic and learning factors also contribute.

First-line treatments are exposure and response prevention—a form of cognitive-behavioral therapy—and certain serotonergic medications. Both can substantially reduce symptoms. OCD is distinct from ordinary perfectionism or carefulness; it is an illness that traps the person in a cycle of doubt and neutralization. Effective treatment interrupts that cycle.

• Unwanted intrusive thoughts and repetitive rituals
• Recognized by the person as excessive
• Maintained by temporary anxiety reduction
• Responds to exposure therapy and medication