Whether it is a skinned knee, a pierced ear or a small cut, we all get to see a little bit of our blood from time to time. And no matter who you are, it’s red. But, the veins that carry our blood aren’t red, they’re blue. Have you ever wondered why? To help us get to the bottom of the mystery, we turn to our friends at Wonderopolis.
Before we can get to answering this colorful question, we should first understand the role of veins in our body. Veins are a part of human’s circulatory system. This network runs blood throughout the body from the heart through your arteries and capillaries and finally through your veins which the final stage before the journey begins again.
Blood is always red, but the shade of red depends on how much oxygen is in the red blood cells. When you breathe in, you are filling your blood cell with oxygen, and it gives them a very bright red color. As blood travels through your body, it loses the oxygen and takes on carbon dioxide (which you exhale). This oxygen-low blood is a darker shade of red.
So why, if the blood in our veins is a dark red, do we see blue color just under the surface of our skin? We’ll let Wonderopolis explain:
“It all has to do with the science of light. The colors we see are the result of which wavelengths of light are reflected back to our eyes. Veins appear blue because blue light is reflected back to our eyes. ...
Blue light does not penetrate human tissue as deeply as red light does. As a result, veins that are close to the surface of the skin will be more likely to reflect blue light back to the eye.”
In short, our veins appear blue because of a trick that light plays on our eyes and how the light interacts with our body and skin. All color works this way as light is a combination of all colors and when it reflects off of certain materials, it absorbs some colors and bounces back others to our eyes.
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