“Blood is blue inside your body”

Many people mistakenly believe that blood circulating through our bodies is blue, only turning red upon exposure to air. The truth is, human blood is always red, regardless of its oxygen content. This vibrant color comes from hemoglobin, an iron-rich protein found in red blood cells. When hemoglobin is bound with oxygen, the blood appears a bright, cherry red. As oxygen is delivered to the body's tissues and the blood becomes deoxygenated, it takes on a darker, deeper red hue, but it never turns blue.

The widespread misconception that blood is blue inside the body often stems from observing the blue or greenish appearance of veins visible just beneath the skin. This visual effect, combined with some older biological diagrams that depicted deoxygenated blood vessels in blue, has reinforced the myth over time.

However, the blue color of veins is merely an optical illusion. When light hits the skin, different wavelengths are absorbed and reflected. Red light, which has longer wavelengths, penetrates deeper into the skin and is absorbed by the red blood in the veins. Blue light, with its shorter wavelengths, does not travel as deeply and is reflected back to our eyes. This scattering and absorption of light by the skin and the blood vessels create the perception that veins are blue, even though the blood flowing within them remains distinctly red.