Blood phobia is the extreme and irrational fear of blood

Blood

Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....

. Acute cases of this fear can cause physical reactions that are uncommon in most other fears, specifically vasovagal syncope

Vasovagal syncope

A vasovagal episode or vasovagal response or vasovagal attack is a malaise mediated by the vagus nerve. When it leads to syncope or "fainting", it is called a vasovagal syncope, which is the most common type of fainting.There are a number of different syncope syndromes which all fall under the...

 (fainting). Similar reactions can also occur with trypanophobia

Trypanophobia

Trypanophobia is the extreme fear of medical procedures involving injections or hypodermic needles. It is occasionally referred to as aichmophobia, belonephobia,...

 and traumatophobia. For this reason, these phobias are categorized as "blood-injection-injury phobia" by the DSM-IV

Diagnostic and Statistical Manual of Mental Disorders

The Diagnostic and Statistical Manual of Mental Disorders is published by the American Psychiatric Association and provides a common language and standard criteria for the classification of mental disorders...

. Some early texts refer to this category as "blood-injury-illness phobia."

Etiology

Blood phobia is often caused by direct or vicarious trauma in childhood or adolescence. Though some have suggested a possible genetic link, a study of twins suggests that social learning and traumatic events, rather than genetics, is the primary problem.

Treatment

The standard approach to treatment is the same as with other phobias - cognitive-behavioral therapy, desensitization, and possibly medications to help with the anxiety and discomfort.  In recent years, the technique known as applied tension, applying tension to the muscles in an effort to increase blood pressure, has increasingly gained favor as an often effective treatment for blood phobia associated with drops in blood pressure and fainting.