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Is blood really blue?

In many TV shows, diagrams and models, deoxygenated blood is blue. Even looking at your own body, veins appear blue through your skin. Some sources argue that blood from a cut or scrape starts out blue and turns red upon contact with oxygen. Other sources say that blood is always red.

It’s time to settle the debate once and for all.

Where did the idea of blue blood come from?

The confusion about blood’s colour started in the 19th century, when the term “blue blood” was used to describe Aristocrats—white, upper-class, Europeans. At the time, these aristocrats and the European royalty spent most of their time indoors and their blue-looking veins could easily be seen through their pale skin. In addition to pale skin, silver was considered a sign of wealth, so those who could afford it had goblets and utensils made of silver. Since these items were in close contact with food and drink, some of the metal was ingested. Ingestion of high amounts of silver can result in Argyria, a skin condition that literally turns your skin greyish blue. The combination of blue looking veins and greyish blue skin gave good reason to the perception that royal blood was blue.

Why is our blood coloured, anyway?

Red blood cells contain hemoglobin, a protein with red pigment that carries oxygen. When hemoglobin picks up an oxygen molecule, its shape changes to hold the oxygen. This conformation of the protein absorbs and reflects certain wavelengths of light to look bright red. When hemoglobin releases oxygen, its shape is modified and appears darker red. Oxygenated or not, your blood is always red. 

So, why are my veins blue?

Veins are not blue.  They only look blue because when wavelengths of light hit your skin and veins, some light is absorbed, and some reflected back at you. Wavelengths of blue light cannot penetrate skin as well as red light, and more blue wavelengths are reflected back at you than red wavelengths. As a result, the veins you can see through your skin look blue

Is blood really blue?

Unless you’re a horseshoe crab or an octopus, your blood is not blue. The veins you can see through your skin look blue because of the way that your skin and veins absorb and reflect different wavelengths of light. While the shade of red may vary depending on how much oxygen your red blood cells are carrying, your blood is red, both outside and inside your body.

Bodies are amazing! If you’re like us and can't get enough of life sciences, then you will love these other posts: Bizarre Brains of the Animal Kingdom and Octupus Genome Untangled