The short answer is no, there is no difference between black blood and white blood. Blood inside the body is always red in color. The red color comes from hemoglobin, the protein in red blood cells that carries oxygen from the lungs to tissues and organs throughout the body. Hemoglobin contains iron, which gives blood its red hue.
What Gives Blood Its Red Color?
Hemoglobin is a protein inside red blood cells that contains iron. It’s the iron that gives blood its red color. Hemoglobin binds to oxygen in the lungs, forming oxyhemoglobin, which is still red. It’s only when hemoglobin gives up its oxygen that it changes to a dark red or purple color. This deoxygenated blood is what makes veins look blue underneath the skin.
Blood is never blue or white inside the body. The different colors we associate with blood actually refer to where blood is carrying oxygen:
- Bright red: Oxygen-rich blood (arteries and oxygenated blood)
- Dark red: Oxygen-poor blood (veins and deoxygenated blood)
The changing color has to do with how light absorbs and reflects off hemoglobin and oxyhemoglobin molecules. Oxyhemoglobin reflects more red light, making it appear bright red. Deoxyhemoglobin absorbs more red light, making it look darker.
Where Does the Idea of Blue Blood Come From?
The notion that some people have “blue blood” stems from the fact that veins under the skin appear blue. This bluish tint comes from how light penetrates the skin and interacts with deoxygenated blood.
When blood returns to the heart through the veins, it has given up much of its oxygen to provide energy to the tissues. With less oxygen bound to hemoglobin, the blood takes on a darker red hue. Light reflects off the blood and through the skin in a way that makes veins look blue.
But the blood inside those veins is still red. The bluish color is only an optical effect.
The Origins of “Blue Blood”
The idea of blue blood entered popular culture in Medieval Spain. Based on their pale skin and the blue veins visible underneath, the nobility claimed their blood was blue. Some even asserted their blood was blue because it had been darkened by the sky and heavens.
Of course, their blood was red like everyone else’s. But calling themselves “blue bloods” helped separate the ruling class from common people and their red blood.
Over time, having “blue blood” came to mean being of noble birth or high social status. Even today, the phrase continues to signify aristocracy and royal lineage.
Can Blood Ever Appear Blue?
In rare cases, blood can take on a blue hue in certain parts of the body. This is called saturm, a condition where hemoglobin binds to excess sulfur molecules in red blood cells.
The sulfur changes the way light is absorbed and reflected, causing blood to look blue, green, black, or other abnormal colors. Saturm usually only affects veins or skin underneath the surface.
Causes of saturm can include:
- Liver disease
- Intestinal infection
- Food preservatives like nitrates
- Genetic disorders affecting hemoglobin
But even with saturm, blood deeper inside the body maintains its normal red color.
The Difference Between Arterial and Venous Blood
While all blood is red, there are some differences between arterial blood and venous blood:
| Arterial Blood | Venous Blood |
|---|---|
| Flows away from the heart | Flows toward the heart |
| High in oxygen | Low in oxygen |
| Bright red color | Dark red color |
| Pumps from heart arteries | Returns to heart veins |
| Pressure is high | Pressure is low |
The key difference is arterial blood has more oxygen, which gives it a brighter red hue. Venous blood is darker from having less oxygen after delivering it to tissues.
Is There Such a Thing as White Blood?
There is no such thing as white blood normally found in the human body. However, white blood cells are an important component of blood.
White blood cells, also called leukocytes, are part of the immune system. They help defend the body against infection from foreign organisms like bacteria, viruses, and fungi.
There are several types of white blood cells, including:
- Neutrophils – Fight bacterial infections
- Eosinophils – Respond to allergens and parasites
- Basophils – Involved in inflammatory responses
- Lymphocytes – Remember past infections to target recurring ones
- Monocytes – Engulf and digest dead cells and pathogens
While white in name, these cells are actually colorless or a pale bluish when viewed under a microscope. They are also far less numerous than red blood cells.
Having too many or too few white blood cells can indicate an underlying medical condition. A high white blood cell count may signal an infection, while a low count may suggest an immune disorder.
Conclusion
Blood is always red while inside the body, no matter where it is located. The red color arises from hemoglobin’s iron content.
Blue or white blood only exists in medical myths and creative metaphors. Real blood maintains its bright or deep red hue whether it’s carrying oxygen in arteries or circulating deoxygenated back through veins.
The next time you get a cut, expect to see red blood cells rather than blue or white ones! Discovering any other colors could mean there’s an unusual medical condition causing abnormal changes to the blood.