Blood in Your Veins Is Not Blue -- Here's Why It's Always Red

[Judi Lynn]

By Marisia Fikiet, University at Albany, State University of New York and Igor Lednev, University at Albany, State University of New York | June 3, 2018 10:02 am ET

Human blood is red because of the protein hemoglobin, which contains a red-colored compound called heme that's crucial for carrying oxygen through your bloodstream. Heme contains an iron atom which binds to oxygen; it's this molecule that transports oxygen from your lungs to other parts of the body.

Chemicals appear particular colors to our eyes based on the wavelengths of light they reflect. Hemoglobin bound to oxygen absorbs blue-green light, which means that it reflects red-orange light into our eyes, appearing red. That's why blood turns bright cherry red when oxygen binds to its iron. Without oxygen connected, blood is a darker red color.

Carbon monoxide, a potentially deadly gas, can also bind to heme, with a bond around 200 times stronger than that of oxygen. With carbon monoxide in place, oxygen can't bind to hemoglobin, which can lead to death. Because the carbon monoxide doesn't let go of the heme, your blood stays cherry red, sometimes making a victim of carbon monoxide poisoning appear rosy-cheeked even in death.

Sometimes blood can look blue through our skin. Maybe you've heard that blood is blue in our veins because when headed back to the lungs, it lacks oxygen. But this is wrong; human blood is never blue. The bluish color of veins is only an optical illusion. Blue light does not penetrate as far into tissue as red light. If the blood vessel is sufficiently deep, your eyes see more blue than red reflected light due to the blood's partial absorption of red wavelengths.Sometimes blood can look blue through our skin. Maybe you've heard that blood is blue in our veins because when headed back to the lungs, it lacks oxygen. But this is wrong; human blood is never blue. The bluish color of veins is only an optical illusion. Blue light does not penetrate as far into tissue as red light. If the blood vessel is sufficiently deep, your eyes see more blue than red reflected light due to the blood's partial absorption of red wavelengths.

More:
https://www.livescience.com/62724-blood-in-your-veins-not-blue.html