Claustrophobia is a fear of confined spaces. It is triggered by many situations or stimuli, including elevators, especially when crowded to capacity, windowless rooms, and hotel rooms with closed doors and sealed windows. Even bedrooms with a lock on the outside, small cars, and tight-necked clothing can induce a response in those with claustrophobia. It is typically classified as an anxiety disorder, which often results in panic attacks. The onset of claustrophobia has been attributed to many factors, including a reduction in the size of the amygdala, classical conditioning, or a genetic predisposition to fear small spaces.