Debunked Myths

The belief that venous blood is blue represents one of biology's most visually persistent myths, reinforced by textbook diagrams showing red arteries and blue veins. The logic seems compelling: oxygen-rich blood is bright red, so oxygen-poor blood must be its opposite color. However, this is purely an illusion of light physics and human perception. Blood is never blue—it ranges from vibrant scarlet when oxygenated to a deep, burgundy red when deoxygenated.

The blue appearance of veins results from how light interacts with skin tissue. Skin scatters and absorbs red wavelengths while allowing blue light to penetrate slightly deeper. When we look at veins, we're seeing blue light reflected back from the tissue above the blood vessel, not the color of the blood itself. Anyone who has donated blood or had blood drawn witnesses the dark red blood filling the vial, never blue.

This myth endures because it creates a neat, color-coded system that seems intuitively correct. The reality is more fascinating: the colors we perceive aren't inherent properties but complex interactions between light, biology, and perception. Our veins aren't blue highways carrying blue blood—they're tunnels viewed through a biological filter that paints them in cool tones, hiding their true crimson cargo.