Specific Phobia

Martin M. Antonya; David H. Barlowb    a St. Joseph’s Hospital and McMaster University, Hamilton, ON, Canada;
b Center for Anxiety and Related Disorders at Boston University, USA

Introduction

In DSM-IV (APA, 1994), a specific phobia is defined as a marked and persistent fear that is cued by the presence or anticipation of a specific object or situation. The fear must be recognized by the individual to be excessive or unreasonable, must be associated with functional impairment or subjective distress, and is typically accompanied by an immediate anxiety response and avoidance of the feared object or situation. In some individuals, phobic avoidance is minimal, although exposure to the situation reliably leads to intense levels of fear. Specific phobias may be differentiated from other phobic disorders based on the types of situations avoided as well as the associated features of the disorder. For example, individuals who avoid a range of specific situations typically associated with agoraphobia (e.g., crowds, driving, enclosed places) are likely to receive a diagnosis of panic disorder with agoraphobia, especially if the focus of apprehension in the feared situation is on the possibility of experiencing a panic attack. Similarly, a person who fears and avoids situations involving social evaluation (e.g., public speaking, meeting new people) is likely to receive a diagnosis of social phobia. In DSM-IV, a diagnosis of specific phobia is not assigned if the fear is better accounted for by another mental disorder.

DSM-IV includes five main specific phobia types: animal type, natural environment type, blood–injection–injury type, situational type, and other type. The introduction of these types was based on a series of reports to the DSM-IV Anxiety Disorders Work Group (e.g., Craske, 1989; Curtis, Himle, Lewis & Lee, 1989) showing that specific phobia types tend to differ on a variety of dimensions including age of onset, gender composition, patterns of covariation among phobias, focus of apprehension (i.e., anxiety over physical sensations), timing and predictability of the phobic response, and type of physical reaction during exposure to the feared object or situation.

Phobias from the animal type may include fears of any animal, although animals that are commonly feared include snakes, spiders, insects, dogs, cats, mice, and birds. Animal phobias typically begin in childhood and tend to have an earlier age of onset than other phobia types (Himle, McPhee, Cameron & Curtis, 1989; Marks & Gelder, 1966; Öst, 1987). In addition, they more common among women than men, with percentages of patients who are female ranging from about 75% in epidemiological studies (Agras, Sylvester & Oliveau, 1969; Bourdon, Boyd, Rae, Burns, Thompson & Locke, 1988) to 95% or more in studies of clinical patients (Himle et al., 1989; Marks & Gelder, 1966; Ost, 1987). Among women, animal phobias are the most common type of specific phobia (Bourdon et al., 1988).

Natural environment phobias include fears of storms, water, and heights. These fears are quite common; in fact, among men, height phobias are the most commonly reported specific phobia (Bourdon et al., 1988). Natural environment fears tend to begin in childhood, although there is some evidence that height phobias begin later than other phobias from this type (Curtis, Hill & Lewis, 1990). Large epidemiological studies have found that storm and water phobias are more common among women than men. For example, anywhere from 78% (Bourdon et al., 1988) to 100% (Agras, Sylvester & Oliveau, 1969) of individuals with storm phobias tend to be female. With respect to sex ratio, height phobias appear to be different than other natural environment phobias in that only 58% of individuals with height phobias tend to be female (Bourdon et al., 1988). These data, as well as other recent findings (e.g., Antony, Brown & Baldwin, 1997a,b) suggest that height phobias may not be typical of the natural environment type.

Blood–injection–injury phobias include fears of seeing blood, receiving injections, watching or undergoing surgical procedures, and other related medical situations. They tend to begin in childhood or early adolescence, and are more common in females, although sex differences are less pronounced than for animal phobias (Agras et al., 1969; Öst, 1987, 1992). Unlike other phobias, blood–injection–injury phobias are often associated with a diphasic physiological response during exposure to the feared situation. This response begins with an initial increase in arousal which is subsequently followed by a sharp drop in heart rate and blood pressure, often leading to fainting. Approximately 70% of individuals with blood phobia and 56% of those with injection phobias report a history of fainting in the feared situation (Öst, 1992). As discussed in a later section, the tendency for individuals with blood and injection phobias to faint has led to the development of specific treatment strategies for preventing fainting in this group.

Situational phobias include specific phobias of situations that are often feared by individuals with agoraphobia. Typical examples include enclosed places, driving, elevators, and airplanes. Situational phobias tend to have a mean age of onset in the twenties (Himle et al., 1989; Öst, 1987); and tend to be more common in women than men. Situational phobias are more likely to be associated with delayed and unpredictable panic attacks in some studies (Antony et al., 1997a; Ehlers, Hofmann, Herda & Roth, 1994), although other studies have found contradictory results (e.g., Craske & Sipsas, 1992).

Finally, an “other type” was included in DSM-IV to describe phobias not easily classified using the four main specific phobia types. Examples of phobias from the “other type” include fears of choking, vomiting, and balloons, although any phobia not easily classified as one of the other four types would be classified in this category.

Overall, specific phobia is the most prevalent anxiety disorder diagnosis and is among the most prevalent of all psychological disorders. Lifetime prevalence estimates for specific phobia are in the range of 14.45 to 15.7 percent for women and 6.7 to 7.75 percent for men (Eaton, Dryman & Weissman, 1991; Kessler et al., 1994). Despite their prevalence, there is still much to learn about the nature and treatment of specific phobias. Although subclinical fears among college students have been studied extensively by investigators seeking to understand the nature of fear and methods of fear reduction, few studies have examined the psychopathology and treatment of specific phobias in clinical patients. Furthermore, the studies that have been conducted tend to focus on a relatively small range of phobias, have small sample sizes, and have not examined differences in treatment response among specific phobia types. Nevertheless, there is increasing evidence that specific phobias are among the most treatable of all disorders. In as little as one session of systematic exposure to the feared situation, the majority of individuals with phobias of animals, blood, and injections are able to overcome their phobias (Öst, 1989).

Theoretical Foundations of Exposure-Based Treatment

Exposure to the feared object or situation is believed to be an essential component of any successful treatment for specific phobia (Marks, 1987), although the mechanisms by which exposure exerts its effects are unclear. Barlow (1988) summarized some of the major theories to explain the process of fear reduction. First, habituation was proposed by Lader & Wing (1966) to explain the therapeutic effects of systematic desensitization. Habituation is the process of becoming familiar with and thereby responding less to a particular stimulus over time (e.g., as when one becomes less aware of a particular odor after prolonged exposure). This process typically leads to only short term changes in responding and appears to affect physiological responses (e.g., galvanic skin response) more than subjective feelings. The role of learning in habituation is presumed to be minimal. Evidence for the role of habituation in fear reduction is mixed (Barlow, 1988).

A more popular model for explaining the therapeutic effects of exposure has been the process of extinction. Extinction involves the weakening of a conditioned response by discontinuing reinforcement. According to Mowrer’s (1960) two-stage model of fear development, a fear (e.g., a dog phobia) begins when a neutral stimulus (e.g., a dog) is paired through classical conditioning with an aversive unconditioned stimulus (e.g., being bitten). According to Mowrer, fear is maintained by negative reinforcement resulting from avoidance of the conditioned stimulus. In other words, avoidance prevents the aversive symptoms associated with the feared object from occurring and is thereby reinforced operantly. In theory, exposure puts an end to the negative reinforcement associated with avoidance and thereby leads to extinction of the fear. Extinction is presumed to involve new learning (i.e., changes in the way information is processed), and tends to have lasting effects, relative to habituation. Nevertheless, there...