Blood-injection-injury type phobia

According to the DSM-IV classification of mental disorders blood-injection-injury type phobias constitute a subtype of specific phobias. It includes fear of blood (hemophobia), injury phobia and fear of receiving an injection (trypanophobia and some other names) or other invasive medical procedures.

A distinctive feature of phobias of this type is their vasovagal manifestation. For most fears (both normal and abnormal) the response to the feared stimulus includes the accelerated heart rate. In the cases of blood-injection-injury phobias a two-phase vasovagal response is observed: first a brief acceleration of heart rate, then its deceleration, bradycardia, and dropped blood pressure. The above may also lead to vasovagal syncope (fainting).

The initial phase of the vasovagal response characterized by this phobia involves activation of the sympathetic nervous system, which results in physiological symptoms such as accelerated heart rate, sweating and shortness of breath. The resulting vasovagal syncope is thought to be a result of the second phase. The second phase involves the activation of the parasympathetic nervous system, which involves the heart rate slowing. The parasympathetic activation is believed to be associated with the disgust response, which is a characteristic of blood-injection-injury type phobias, making it stand out from other phobias.

The vasovagal syncope response is not present in all patients with a blood-injection-injury type phobia. People with blood-injection-injury type phobias with the syncope are shown to have an underlying autonomic dysregulation. This dysregulation predisposes them to the syncope when exposed to the stimulus. People with these dysregulations are shown to have fainting episodes even when they are not directly injected or harmed.

FMRI studies also show that there is less prefrontal cortex activation in people with this type of phobia when exposed to a fear-inducing stimuli. The prefrontal cortex is involved in controlling and regulating emotions. This shows that people with a blood-injection-injury type phobia have less control over their emotions because of the lessened activity in their prefrontal cortex. This lessened emotional control could contribute to the high disgust reaction as well as less control over the phobic symptoms (fainting).

These characteristic vasovagal reactions may contribute to the development of a phobia.

The other factors contributing to the development of the blood-injection-injury phobias are the same as for other specific phobias.