What causes Obsessive Compulsive Disorder?

The short answer is that we don't really know. There is general consensus that it is a neurobiological disorder, which in plain English means that OCD is caused by a glitch in how your brain works. It is as if a circuit refuses to close and the person with OCD cannot break out of an endless loop. Some people have referred to this as a "brain hiccup". We used to think OCD was related to unresolved inner conflicts or from poor parenting, but these theories have not received much research support.