Deoxygenated blood is a darker red color. While often mistakenly perceived as blue, human blood is always red, its shade varying depending on oxygen levels.
The Role of Oxygen and Hemoglobin
The color of blood is primarily determined by hemoglobin, a protein in red blood cells that carries oxygen. Hemoglobin bound to oxygen (oxygenated blood) absorbs blue-green light and reflects red-orange light, resulting in the bright cherry red color we associate with arterial blood. When hemoglobin is not bound to oxygen (deoxygenated blood), it reflects less red light, appearing a darker shade of red. This darker red color is still distinctly red and not blue.
Why the Misconception of Blue Blood?
The misconception that deoxygenated blood is blue likely stems from the superficial appearance of veins. Veins appear blue due to the way light interacts with the skin and the blood within the veins, not because the blood itself is blue.
Scientific Consensus
Multiple reputable sources, including medical journals and educational institutions (Medical News Today, The Conversation, Cleveland Clinic), confirm that all human blood is red, with variations in shade depending on oxygen saturation. Deoxygenated blood is a darker red, not blue.
Examples of Blood Color Variations
- Oxygenated blood: Bright cherry red.
- Deoxygenated blood: Darker red.
