The US classification for mental health disorders, DSM-V, defines this as a marked and out of proportion fear within an environmental or situational context to the presence or anticipation of a specific object or situation. When a phobic person is exposed to the situation, it provokes an immediate anxiety response, which may take the form of a panic attack. In distinguishing a phobia from a reasonable fear, the criteria include that the person recognizes that their fear is out of proportion; they avoid the phobic situation or endure it with intense anxiety or distress; furthermore, these symptoms interfere significantly with their normal routine, occupational (or academic) functioning, or social activities or relationships.

Treatment is COGNITIVE BEHAVIOUR THERAPY (CBT) (more recently complemented by exposing the person to virtual reality sessions of their phobia). In some patients ANTIDEPRESSANT DRUGS are prescribed. (See also MENTAL ILLNESS.)