I’ve known people that easily faint at the slightest sight of blood, they don’t necessarily have to be the one bleeding, just seeing a little bit from someone else causes them to faint. How can something that small causes your whole body to shut down?
In: Biology
What you describe is known as “reflex syncope” or “vasovagal syncope”. Some people (especially boys and young man) pass out after they see blood. Often this effect is triggered by excitement or nervousness: It causes your heart rate and your blood pressure to increase and to decrease again suddenly afterwards. Combined with the sight of blood it is an overreaction to a threatful situation: Your brain sees blood and thinks you are bleeding. The drop in blood pressure after the initial excitement causes a undersupply of blood in your brain. The physiological reaction is to widen your blood vessels in your legs and to overturn your body in order to accomplish a blood flow in important body regions (brain, heart, internal organs) and to stay alive. Now, when your blood vessels in the legs are dilated, your blood pressure drops even more and the brain is completely unprovided with blood for a short time. This is what causes you to faint (a syncope).
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