Why Is Blood Red?

Thu, 10 Apr 2025 22:06:12 +0000

It’s a question that's been pondered for centuries. It's such an obvious question, in fact, that it barely even seems worth asking anymore. But it is worth asking! And the answer is actually pretty interesting. So let's get into it!
The quick and simple answer is that blood absorbs green light and reflects red light. As a result, it appears red to your eye.
This means that the reason why the blood looks red is because of how light is reflected through our body!

Blood is red because of hemoglobin, a protein molecule that contains iron. When the oxygen in your blood comes in contact with this iron and binds to it, it gives off a reddish color.
Hemoglobin helps transport oxygen throughout the body through arteries and veins. Hemoglobin is what gives blood its dark red color. Red light can't pass through a water molecule because of its electric charge, but green light can: it reflects off the surface of water molecules instead of being absorbed by them. That’s why if you’ve ever dived down deep in the sea, you’ll notice that reds quickly disappear, but greens can still be seen clearly.
The amount of red light can change with temperature too though.
Hemoglobin absorbs light energy (also known as photons) and converts it into heat energy instead. When there's more hemoglobin present than necessary, those extra photons are absorbed by free electrons in other molecules within our cells; this leads to higher temperatures and eventually causes overheating if conditions get too extreme (like on hot summer days). On the flip side, when there isn't enough hemoglobin available for this process due to insufficient oxygen levels or injuries like cuts from sharp objects like knives--it results in a blue discoloration because not enough light is getting through due an absence or deficiency of iron-containing proteins such as myoglobin.

So next time you hear someone tell you that blood is actually blue when it doesn’t have enough oxygen, you can tell them that they’re wrong, and that the blood is always red, but that the colour we see depends on a number of factors, including how much hemoglobin there is in the blood, how much light there is, the colour of the light, and even the temperature.