Why Is Human Blood Red? The Science Explained 🩸

Added: 2026-05-21

[00:00:00]Why is blood red? It comes down to a single molecule, hemoglobin.

[00:00:05]Inside your red blood cells, hemoglobin binds oxygen.

[00:00:10]At its core is iron. When oxygen attaches to iron, it changes how light is absorbed and reflected. More red wavelengths are reflected back. That's why oxygen-rich blood appears bright red. When oxygen is low, the color becomes darker.

[00:00:27]So, blood isn't just red by chance. It's the chemistry of iron interacting with oxygen inside every cell.