Anxiety Shorts: Why Do I Faint When When I See Blood?

As a kid, I remember being scared of needles. It all started when I was at school waiting to receive what I think was my tuberculosis injection. We were all lined up outside, and the older kids were having their injections first. They would then walk past us talking loudly about how they, “felt the needle poke into their bone,” or how the pain was “intolerable.” Jerks!

However, some people experience much stronger reactions to needles or the sight of blood. In fact, most people know someone who faints when they see blood or needles. This reaction can range from annoying or embarrassing to quite interfering (for example, if you’re trying to be a doctor). But why does it happen at all? It seems to make no sense, especially from an evolutionary perspective, as it doesn’t seem that fainting would help you in any way!

What is the Cause of Fainting?

It turns out we have a reflex in the brain that is triggered when we are at risk of losing blood (such as if we get wounded), or at the mere sight of blood for some people. This reflex is called the “vasovagal response.” This is just your parasympathetic system activating, which does two things. It slows your heart rate, and it causes blood vessels to dilate. This drops blood pressure and you faint because not enough oxygen is getting to your brain.


Fainting conveniently means you fall to the floor so it’s easier to get blood back to your brain. It’s also suggested that this drop in blood pressure is there to stop you bleeding more. Both of these things are meant to keep you alive, so in fact it’s a really good bodily response! I’ve even read somewhere that the fainting response may be used to make others thing you’re dead, like some animals do, but this seems like a bloody stretch to me. That’s a bad English pun!

There is a Quick Fix

If you’re someone who gets dizzy or faints there’s actually something you can do. It’s called “applied tension” and is simply contracting muscles to increase your blood pressure and counter this drop. To do this, some people clench their fists and arms, but I’ve heard that pushing your thighs together is actually more effective. Doing this simple technique is part of initial treatment for needle-blood phobia to help get through initial exposures without fainting.

I hope you found it an interesting read. If you have any suggestions for topics you want me to discuss, please send me an email at!

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