There is no single established cause of OCD. However, researchers believe the
disorder has a neurological foundation (i.e., it starts in the brain) and may
be inherited. Current research is examining the role of a chemical messenger
called serotonin in the brain and is looking at how different parts of the brain
communicate with each other. Researchers are also looking into whether the immune
system may be involved in causing OCD.
Approximately 50% to 70% of people with OCD first develop symptoms of the disorder
after a stressful life event, such as a death in the family or job loss. However,
researchers are uncertain of how stress may trigger the onset of OCD.