Obsessive–Compulsive Disorder (OCD) is an anxiety disorder characterized by intrusive thoughts that produce anxiety, by repetitive behaviors aimed at reducing anxiety, or by a combination of such thoughts (obsessions) and behaviors (compulsions). Symptoms may include repetitive hand-washing; extensive hoarding; preoccupation with sexual or aggressive impulses, or with particular religious beliefs; aversion to odd numbers; and nervous habits, such as opening a door and closing it a certain number of times before one enters or leaves a room.