Natural human uneasiness about blood, injury, or deformity sometimes
becomes a specific phobia, which can lead to serious disability if vital
medical procedures are refused. Blood-injury phobia usually starts in
childhood and is often familial. Unlike other phobic cues, which cause
persistent tachycardia, blood-injury phobic cues evoke an initial rise in
heart rate followed by vasovagal bradycardia and, frequently, syncope.
Although blood-injury phobia may have an evolutionary, genetic, and
physiological basis, it can be treated effectively by exposure. The
tendency to faint early in exposure therapy can be reduced by lying down,
tensing the muscles, or inducing anger.