Phobias are intense, persistent, unadaptive fears that are irrational/excessive. They are commonly classified into three groups: complex phobias, including agoraphobia (fear of public places, travel); social phobias (fear of social situations/scrutiny); and circumscribed phobias, including intense fears of insects, animals, heights, and enclosed spaces.

There are biological contributions to the development of some phobias, but the main determinants appear to be learned. Three main pathways to the acquisition of phobias have been identified. The conditioning acquisition of a phobia results from exposure to a traumatic stimulation or from repeated exposures to aversive sensitizing conditions. The second pathway is vicarious acquisition: direct or indirect observations of people, or of other animals, displaying fear. Among humans the transmission of fear-inducing verbal information is the third pathway. For a considerable time, explanations of the acquisition of phobias were dominated by the conditioning theory, which emphasized the importance of exposure...