Obsessive compulsive disorder, usually known as OCD, is a common mental health condition which makes people obsess over thoughts and develop behaviour they struggle to control.
It can affect anyone at any age but normally develops during young adulthood.
It can cause people to have repetitive unwanted or unpleasant thoughts.
People may also develop compulsive behaviour – a physical action or something mental – which they do over and over to try to relieve the obsessive thoughts.
The condition can be controlled and treatment usually involves psychological therapy or medication.
It is not known why OCD occurs but risk factors include a family history of the condition, certain differences in brain chemicals, or big life events like childbirth or bereavement.
People who are naturally tidy, methodical or anxious are also more likely to develop it.