Why Is Blood Red? Does It Have to Be Red?

(Last Updated On: March 29, 2019)

Why Is Blood Red? Does It Have to Be Red?

Why is Blood Red?

Well, the short answer is red blood cells. But there’s a lot more to “why is blood red” than the little donuts floating around in blood plasma. Foremost, red blood cells account for about 40% of your blood’s total volume, and 55% of total blood composition is the plasma that transports blood cells. So case closed, red blood cells make up most of the cell volume in our blood and therefore blood is red, right?

There’s still more to it than that, hence the common misconception of blood turning blue. It’s common knowledge that people need oxygen to live, and oxygen gets to different parts of the body through red blood cells. It’s also common knowledge that oxygen isn’t red, so where does the red in “red blood cell” come from?

Red blood cells are mostly hemoglobin, which in short binds to the oxygen we breathe and carries it to the parts of the body that need it (hemoglobin does this in part because of iron, which is why blood tastes vaguely like metal). It’s blood that’s oxygen rich that has its bright red color, and blood that doesn’t have oxygen (making its way back to the lungs) that, while still red, is often duller in color. Basically, your blood is red because of iron, and that’s pretty metal.

Is All Blood Red?

No, only animals with iron rich blood (like humans and other vertebrates) have red blood. Blood itself is just a vehicle to transport oxygen throughout the body, and it’s not going to be red if the protein that transports oxygen isn’t red by nature.

Look at squids, crabs, and other arachnids. Their blood contains hemocyanin, which unlike hemoglobin, transports oxygen by way of copper instead of iron. Copper is blue, and so is their blood. Some other marine invertebrates transport oxygen with hemerythrin, which turns violet or pink in the presence of oxygen. Some worms color their blood with chlorocruorin, which when exposed to oxygen in low concentrations is green.

But perhaps most interesting are beetles and sea cucumbers, who don’t color their blood with oxygenated metals. These animals also transport their oxygen with hemocyanin, but they actually have yellow blood. This yellow comes from vanabin proteins, which are actually higher in concentration within their blood than the oxygen transporting hemocyanin. As the name implies, these proteins contain a lot of vanadium–which turns yellow when exposed to oxygen. No, nobody really knows why these animals collect so much vanadium, but the current running theory is that the vanadium could make their blood toxic to predators.

Can I Change the Color of My Blood?

Believe it or not, precedent actually exists for people changing their color with the power of metal. Paul Karason was known for drinking colloidal silver before he passed away–which turned his skin blue. Blood and skin are a little different though, and in theory you could change the color of your blood the same way those beetles do with vanadium if this post is anything to go by.

In practice of course, adding a bunch of metal to your own blood sounds like a really good way to give yourself hypercoagulative (very thick) blood, and introducing a foreign compound to your body sounds like a worse way to poison yourself. But we suppose this operates under the principle of “anyone can swim in a volcano, once.”

So you should let that iron do its thing, and avoid drinking metal where you can.

Warning: We here at Sporcle though do not condone the changing of one’s blood hue for recreational or any other purposes.

Like blood and all things hematology? Test your ability to determine blood types here.

About the Author:

+ posts

Kyler is a content writer at Sporcle living in Seattle, and is currently studying at the University of Washington School of Law. He's been writing for Sporcle since 2019; sometimes the blog is an excellent platform to answer random personal questions he has about the world. Most of his free time is spent drinking black coffee like water.