Blood is NEVER blue — veins look blue because of how light penetrates skin
Deoxygenated blood is dark red, not blue. The myth that blood is blue before it hits air comes from the blue appearance of veins beneath the skin. The truth is an optical effect: different wavelengths of light penetrate skin to different depths. Blue and violet light is absorbed near the surface, while red light penetrates deeper. The vein itself appears blue-ish because of how the contrast between absorbed and reflected light reaches our eyes. Blood drawn from a vein is visibly dark red immediately — it was never blue.
This myth is taught as fact in many schools and is reinforced by the blue colour used for veins in medical diagrams. Discovering the actual mechanism — that it's a skin optics illusion, not a chemical property — makes the body feel more optically complex than expected.
“Blood is never blue. Veins look blue because of how skin absorbs different light wavelengths. Deoxygenated blood is dark red. Blood drawn from a vein is immediately dark red — it was never blue. 🔵➡️🔴 #OddlyHuman”