The "Blue Blood" Myth: Why Veins Look Blue but Blood Never Is
Blood is always red (bright when oxygenated, dark maroon when deoxygenated). Veins look blue due to Rayleigh light scattering through skin — the same physics that makes the sky blue.
Human blood is ALWAYS red — it is never blue at any point. This myth is widely taught in schools, even by health teachers, but it is completely false. The two colors of blood: - Oxygenated blood (arteries): bright red - Deoxygenated blood (veins): dark red/maroon — NOT blue Why veins appear blue through skin: - Light scattering through multiple skin layers preferentially reflects shorter (blue) wavelengths back to your eyes - This is the same Rayleigh scattering effect that makes the sky appear blue - The vein itself and the blood inside are not blue — it's an optical illusion created by how light interacts with tissue Why the myth persists: - Medical diagrams traditionally color arteries red and veins blue for easy visual distinction - The more "sophisticated" version ("blood turns blue when it loses oxygen") sounds scientifically plausible - Once learned in childhood, the myth is rarely corrected - Many teachers were themselves taught the myth and pass it on confidently Proof: If you draw blood from a vein (deoxygenated blood), it comes out dark red, not blue. Blood exposed to air doesn't "turn red from oxygen" — it was already red.