Adrenaline constricts blood vessels in your skin to reduce bleeding during injury, redirecting blood to vital organs.

The sympathetic nervous system triggers the adrenal glands to release epinephrine—commonly called adrenaline—in response to perceived threats. This hormone binds to alpha-adrenergic receptors in peripheral blood vessels, narrowing them through a process called vasoconstriction. By reducing blood flow to the skin and extremities, the body minimizes potential blood loss during physical injury.This blood flow redirection serves a dual purpose: it protects against bleeding while optimizing survival resources. The body prioritizes oxygen-rich blood to skeletal muscles, lungs, and brain, enhancing physical performance and reaction time. This is why people under acute stress often develop a pale complexion or cold fingers and toes—surface temperature drops as circulation to the skin decreases.Research documented in journals like Psychosomatic Medicine shows this vascular response occurs within milliseconds of a perceived threat. Walter Cannon, the Harvard physiologist who first described the fight-or-flight response in 1915, recognized these changes as essential for survival. Modern studies using Doppler ultrasound confirm that blood flow to the skin can decrease by more than 50 percent during acute stress, effectively redirecting that volume to the body's core.