Obsessive–compulsive disorder
The cause of obsessive–compulsive disorder is unknown. There is evidence that genes have a strong role in developing the disorder. If the disorder starts in childhood, it is more likely that other family members will have OCD than if the disorder starts in adulthood. It is thought that obsessive–compulsive disorder is the result of things humans did when they were evolving. Stress-inducing events also make OCD more severe.