The concept of blue blood, especially in humans, is fake.
Despite common misconceptions, human blood is always red. The idea of blue blood likely comes from a misunderstanding of how veins appear through the skin, sometimes making them look bluish.
Why is Blood Red?
Human blood gets its red color from hemoglobin, a protein in red blood cells that contains iron. When hemoglobin binds with oxygen, it appears bright red. When blood loses oxygen, it becomes a darker red, but it is never blue.
The Color Difference Explained:
| Feature | Oxygenated Blood | Deoxygenated Blood |
|---|---|---|
| Color | Bright Red | Dark Red |
| Reason | Oxygen bound to Hemoglobin | Oxygen released from Hemoglobin |
The Misconception of Blue Veins
Veins, which carry deoxygenated blood back to the heart, often appear blue through the skin because of the way light is absorbed and scattered by the skin and tissues. This is an optical illusion; the blood in veins is still red, just a darker shade.
Key Points to Remember:
- Human blood is always red, regardless of oxygen content.
- Veins appear blue due to the way light interacts with skin, not the blood itself.
- The term "blue blood" is a figurative term used in social contexts, not a literal description of blood.
Invertebrates with Blue Blood
While human blood is not blue, there are some invertebrates that have blue blood due to the presence of hemocyanin, instead of hemoglobin. Hemocyanin contains copper instead of iron, which gives their blood a bluish tint when oxygenated. These animals include:
- Crabs
- Lobsters
- Spiders
- Octopuses
- Squids
