Is Blood Blue?


There are a lot of myths about the human body which are sometimes difficult to imagine. Some of them just came from some misconceptions of other people and passed on to others. It is sometimes amusing to think that some people believe certain myths even though there are no proof or evidence that support them. One of those myths is that our blood is not actually red but blue. Have you ever thought about the human blood appearing in color blue?

Our blood is made up of 90 percent water which helps it to flow easily between organs.  It is also composed of different protein and chemicals. One of these is the hemoglobin which gives blood the red color. When combined with oxygen, it produces a bright red color, the kind of red we see when we suffer from cuts. So, where did the idea that blood is blue came from?

Some people believe that blood is blue because of the blue veins that are visible on our body. They think that since the veins appear to be blue, it’s possible that the liquid flowing through them are blue as well. Another reason is the drawings we see in Science and medical textbooks where there are red and blue veins. However, this is not true because our blood is always red. Oxygen-rich blood is bright red and as it leaves the heart and goes through the veins, it is still red, but it becomes much darker because of the absence of oxygen. In the illustrations we see in textbooks, veins are colored in red and blue to distinguish the difference between veins and arteries. If the blood that flows in our body is red, why do the veins we see on our body appear to be blue?

Seeing our veins in blue has something to do with the way the tissue in our skin absorbs, scatters, and reflects light. It is somehow an optical illusion since only certain kinds of light can penetrate our skin. To be more specific, red light can easily penetrate our skin, therefore, the color left to be reflected is blue since blue lights cannot enter deep in our skin, they just stay on the surface. That’s why we see our veins as blue because blue light can be perceived by our eyes more easily compared to red light. Some scientists also explain that blue lights tend to scatter and reflect more easily when it passes through human tissue that’s why veins appear blue even though dark red blood flows through them.

One of the evidence that proves blood is red is when certain accidents occur. For example, when a part of the body has been cut or ripped open, we can see that the blood coming out of the veins are red. Another is when we donate blood, we can clearly see that the blood that is transferred to the bag is red, though darker than what we see during accidents, but it’s still red and never blue.

While it has been proven that the human blood is red, octopuses and horseshoe crabs, on the other hand, are the ones that have blue blood. The reason for this is because the protein responsible for transporting oxygen in their blood, which is called hemocyanin, is in fact blue. Hemocyanin is copper based and it is more efficient at transporting oxygen compared to hemoglobin, when in very low water temperature. Once the copper is mixed with oxygen, it will automatically turn blue.

In humans, there is only one instance that our blood may appear slightly blue. It is when a person suffers from sulfhemoglobinemia. It is a very rare condition in which the blood lacks hemoglobin. When this happens, the blood becomes very dark red with a bluish touch. Being overdosed with medications that contain sulfonamides can be a cause of this condition. Another cause can be occupational exposure to sulfur compounds.

After learning these things about the human blood, we can certainly conclude that our blood is in fact red. It may change color depending on the amount of oxygen it carries. Our blood can be bright red and dark red at times. But remember that it is never going to be blue unless you’re diagnosed with a certain disease.

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