Why Do Some People Faint at the Sight of Blood? The Science Behind Blood-Injection Injury Phobia

Why Do Some People Faint at the Sight of Blood? The Science Behind Blood-Injection Injury Phobia

22 January 2025

Blood-Injection-Injury phobia (BIIP) is a specific anxiety disorder characterised by an atypical physiological response to stimuli such as blood, injuries, or injections. Unlike other phobias that primarily trigger a heightened sympathetic nervous system response, BIIP often leads to a biphasic reaction, culminating in vasovagal syncope or fainting. Understanding the science behind this response sheds light on why some individuals faint at the sight of blood.

The Biphasic Response in BIIP

When individuals with BIIP encounter triggers like blood or needles, their bodies initially react with a typical anxiety response:

  1. Phase One – Sympathetic Activation: 

    Increased Heart Rate and Blood Pressure: The body’s “fight or flight” mechanism activates, leading to elevated heart rate and blood pressure.However, this is swiftly followed by a contrasting second phase:

  2. Phase Two – Parasympathetic Overcompensation: 

    Sudden Drop in Heart Rate and Blood Pressure: The parasympathetic nervous system overcompensates, causing a significant decrease in heart rate and blood pressure.This rapid decline in cardiovascular activity reduces cerebral blood flow, resulting in dizziness, light-headedness, and, in many cases, fainting. Scientific evidence shows that this sequelae is unique to BIIP and is not commonly observed in other phobic reactions.

Genetic and Physiological Underpinnings

Scientific research indicates that individuals with BIIP may have an inherent predisposition to vasovagal syncope. It was found that subjects with blood/injury phobia exhibited underlying autonomic dysregulation, making them more susceptible to neurally mediated syncope.

Moreover, familial patterns suggest a genetic component. Approximately 80% of individuals with needle phobia report a first-degree relative with the same condition, indicating a hereditary link.

Clinical Management

Understanding the unique physiological response in BIIP is crucial for effective management. Techniques such as applied tension, where individuals learn to tense their muscles to maintain blood pressure during exposure to phobic stimuli, have shown promise. Additionally, cognitive-behavioural therapy (CBT) can help individuals desensitise to triggers and learn coping strategies, reducing the likelihood of fainting episodes.

We have an upcoming group-based CBT for children/teenagers with BIIP at Bowyer Psychology. Please contact our friendly administration team to express your interest, and we will get in touch to determine your child’s eligibility for the group therapy.

Why Do Some People Faint at the Sight of Blood? The Science Behind Blood-Injection Injury Phobia
brandmark

Book Appointment

Selected service: