How does de-oxygenated blood turn blue?

The simple answer is it doesn't. Deoxygenated blood is not blue. It's actually dark red. This is one of the most common science myths. The reason many people think deoxygenated blood is blue is because our veins often appear blue through the skin, but the blood flowing inside them is still red.

I remember learning in school that arteries carry red blood and veins carry blue blood. It wasn't until much later that I found out this was just a simplified way of explaining blood circulation and not what actually happens inside our body.

Our blood contains a protein called hemoglobin, which carries oxygen throughout the body.

When hemoglobin is rich in oxygen, the blood appears bright red.

After oxygen is delivered to different organs and tissues, the blood returns to the heart with much less oxygen. At this stage, it becomes dark red, not blue.

So, whether the blood has plenty of oxygen or very little, it's always some shade of red.

How Does the Confusion Happen?

The confusion comes from the way our skin and light interact.

Veins are located just beneath the skin. As light passes through the skin, certain wavelengths are absorbed while others are reflected back to our eyes. This optical effect makes veins appear bluish or greenish, even though the blood inside them remains dark red.

In other words, it's your eyes seeing a color effect, not your blood changing color.

Why Do So Many People Believe This Myth?

Many of us grew up looking at biology diagrams where arteries were colored red and veins were colored blue.

Those colors were only used to make the diagrams easier to understand. They were never meant to show the actual color of the blood.

Because of those illustrations, many people assume veins contain blue blood, which isn't true.

Interesting Facts

Here are a few interesting facts about blood:

• Blood is always red, whether it's oxygen-rich or oxygen-poor.

• Oxygen-rich blood is bright red.

• Oxygen-poor blood is dark red or maroon.

• Veins only appear blue because of the way light interacts with our skin.

• If a doctor draws blood from your vein, you'll see that it's dark red, not blue.

Blood at a Glance

The idea that deoxygenated blood turns blue is one of the most widespread biology myths. In reality, your blood is always red. The only thing that changes is how much oxygen it carries, which affects the shade of red, not the color itself.

Must Read: What is the PH value of human blood?

It is a common misconception that when blood lacks oxygen it turns blue. Probably, people draw this conclusion from the fact that when something like suffocating happens people's lips and complexion seem to turn blue-ish or purple due to lack of oxygen.

People often spread myths that we never see blood in its blue form because the instant we get cut, the blood is exposed to oxygen and thus, instantly turns red. Of course, when you get blood drawn from your veins that isn’t exposed to air, we see that it is dark red, but let’s not let such observations get in the way of a good myth.

In reality, it turns out just dark red when blood is deprived of oxygen. You may have come across the fact that while donating blood your blood looks more bright. When it’s oxygenated, it turns a brighter red. This red color primarily comes from the hemoglobin, which contains four heme groups.

These heme group’s interactions with various molecules end up giving it the dark red or light red color. The hemoglobin itself is a protein that binds with oxygen to eventually be distributed throughout the body in blood.