Blood phobia

Causes

Blood phobia is often caused by direct or vicarious trauma in childhood. Though some have suggested a possible genetic link, a study of twins suggests that social learning and traumatic events, rather than genetics, is of greater significance. Blood-injection-injury phobia (BII) affects about 4% of the population in the United States.

The inclusion of BII within the category of specific or simple phobias in classificatory systems reflects a perception that fear has a primary role in the disorder. Consistent with this assumption, blood-injury phobia appears to share a common etiology with other phobias. Kendler, Neale, Kessler, Heath, and Eaves (1992) have argued from data comparing monozygotic with dizygotic twins that the genetic factor common to all phobias (agoraphobia, social phobia, and specific phobias), strongly predisposes a person to specific phobias.

The recognition of an inherited vulnerability common to all phobias is consistent with the notion that elevated trait anxiety predisposes one to anxiety disorders. Trait anxiety provides a background of affective arousal that permits a more rapid activation of the fight or flight response. With respect to specific activating events, conditioning is one way that stimuli become able to elicit anxiety. It is believed that these changes are controlled by the vagus nerve, which affects activity in the chest and abdomen.

Accordingly, painful experiences can condition fear to blood-injury stimuli. Investigators typically classify around 60% of self-reported onsets of blood-injury phobia as beginning with conditioning experiences. However, examinations of available case-by-case verbal summaries call into question the conclusion that conditioning episodes are as prevalent as reported. For example, Thyer et al. (1985) identified a conditioning episode when a "patient received an injection at age 13 and fainted", and in another person when "at age six she heard her elementary school teacher give a talk on the circulatory system. This frightened the patient to the point of syncope."