Look at the back of your hands. you will most likely see a road system of wavy lines running from your knuckles to your wrist. however, there is a question: why do those blood-filled veins look blue?
It’s a question that gets thrown into the google search engine thousands of times a day, so it’s safe to say people are curious.
so what color is the blood that flows inside your body? Hematologist Alan Lichtin, MD, has the answer.
what color is blood?
There is no need to increase the suspense: blood is red. it can range from a bright cherry red to a dark brick red, but it is always red.
“if you cut yourself,” says dr. lichtin, “red is the only color you’ll see come out.”
the reason? it has to do with the hemoglobin molecules inside the red blood cells. Hemoglobin carries oxygen throughout the body in a fast-moving taxi system that keeps cells and tissues working properly.
Each hemoglobin molecule includes a protein called heme that contains iron. when iron reacts with oxygen, it turns red. that interaction is what gives blood its red color.
Does the blood change color?
In a way, yes, but it always stays in a red hue.
Blood that has just been loaded with oxygen as it flows through the lungs and heart appears bright red, says dr. Lichtina’s heart pumps this oxygen-rich blood to the far reaches of his body. (Fun fact: More than 60,000 miles of blood vessels run through his body.)
As this arterial blood flows through your circulatory system, your body draws in the oxygen it needs. as the oxygen departs, the blood slowly darkens. eventually, it looks muddy red, says dr. lichtina.
This dark, impoverished blood is what you see in the bluish veins under your skin. at that time, venous blood returns to the heart and lungs to reoxygenate.
Your blood, by the way, goes out and back about three times a minute in this amazing process.
Is blood always blue?
Let’s go back to that vein in your hand. when you look at it, you can’t deny the blue hue of it. “That’s an optical illusion created by the way the light passes through the skin and the vein wall,” explains Dr. lichtina “blood is not blue.”
well, at least in humans. blue blood flows through the veins of some living things, including horseshoe crabs and octopuses. (The blood of these animals uses a copper-containing protein called hemocyanin to carry oxygen, which explains the blue color.)
You can even find green blood and purple blood in the animal kingdom, mainly in worms or similar critters. And of course, the fictional character Spock from “Star Trek” bled green… but he was a Vulcan.
a rare condition
While we’re on the green section of the box of crayons, there’s a rare condition called sulfhemoglobinemia that can turn blood that color.
The disorder occurs when a sulfur atom changes the chemical reaction taking place within hemoglobin. the condition is usually caused by medications with sulfur-containing compounds. symptoms include blood that has a dark green tint.
however, the funky color is temporary. As new red blood cells are formed, the blood returns to a more familiar appearance.
the last word
“Blue bloods” is just a term that refers to a noble family lineage or a college athletic team with a winning record. consider it a colorful phrase, not a medical description.
“blood is red”, reiterates dr. lichtina “not much more to say.”
