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Is blood a crimson or scarlet?

Blood is a vital bodily fluid that is responsible for transporting oxygen and nutrients throughout the body while also carrying metabolic waste products away from tissues. The color of blood is an important indicator of health and disease. But is blood crimson or scarlet in color?

The Composition and Function of Blood

Blood is composed of plasma, red blood cells, white blood cells, and platelets. Plasma makes up about 55% of blood and is a yellowish fluid that contains proteins, minerals, vitamins, and glucose. Red blood cells, also called erythrocytes, are responsible for carrying oxygen and giving blood its red color. White blood cells, or leukocytes, help fight infection in the body. And platelets are cell fragments that help blood clot when there is an injury.

When it comes to function, blood transports oxygen from the lungs to tissues all over the body. The hemoglobin molecule contained in red blood cells binds to oxygen, enabling its transport. Blood also moves carbon dioxide back to the lungs so it can be exhaled. Additionally, blood carries nutrients absorbed during digestion to cells for energy production and growth. Waste products like urea are filtered out by the kidneys and excreted in urine.

The Red Color of Blood

As mentioned, it is the red blood cells that give blood its characteristic red color. Red blood cells get their color primarily from hemoglobin, which is a protein containing heme groups with iron atoms. It is the iron atoms that contribute to the red color of hemoglobin and blood.

When blood first comes out of a wound, it appears more of a bright red. This is because the blood is highly oxygenated, with oxyhemoglobin giving it the scarlet red color. As blood sits exposed to air, it starts to turn a darker red. This occurs as oxygen dissociates from hemoglobin, leaving deoxyhemoglobin which has more of a crimson red hue.

The Crimson vs. Scarlet Debate

When it comes to deciding whether blood is truly crimson or scarlet in color, there are a few considerations:

  • Oxygenation – Highly oxygenated arterial blood with lots of oxyhemoglobin appears more scarlet, while deoxygenated venous blood is more crimson.
  • Volume – Blood seen in smaller quantities like from a finger prick may look more crimson, while larger amounts like during blood donation appear scarlet.
  • Individual variation – Factors like diet, hydration status, and underlying health conditions can influence the exact red shade of blood.
  • Lighting – The color and intensity of light can alter blood’s appearance from crimson to scarlet.

Overall, blood exhibits shades of both crimson and scarlet depending on the context. Scarlet is a brighter, more vivid red associated with fresh, oxygen-rich blood. Crimson is darker and richer, linked to deoxygenated blood. But there is no definitive answer since blood can take on both shades.

Crimson and Scarlet in Culture

The crimson and scarlet color of blood has strongly influenced culture and symbolism across human history. Here are some examples:

  • Scarlet was a prestigious color in ancient cultures like Rome, worn by military leaders and the aristocracy.
  • Crimson is connected to suffering and sacrifice, from religious imagery to the “red coats” of British soldiers.
  • The Red Cross and Red Crescent use a scarlet cross/crescent representing care for the wounded.
  • Crimson and scarlet are popular team colors conveying passion and strength.
  • Scarlet letters symbolize adultery from the novel The Scarlet Letter by Nathaniel Hawthorne.

Blood color even appears in common expressions like “caught red-handed” and “see red” when angry. Overall, crimson conveys darker, richer red tones while scarlet is brighter and more vivid.

Conditions Affecting Blood Color

While blood is generally red in color, certain medical conditions can alter its appearance. Here are some conditions that may affect blood coloration:

Condition Color Change Cause
Anemia Paler red Low red blood cell/hemoglobin levels
Polycythemia Darker red High red blood cell count
Carbon monoxide poisoning Cherry red CO binds to hemoglobin
Cyanosis Blue or purple Deoxygenated blood in skin

In addition to the hue, blood consistency and texture may also be affected by conditions like blood clots, infections, and bleeding disorders.


In summary, blood exhibits shades of both rich crimson and vivid scarlet depending on factors like oxygenation, volume, and lighting conditions. While scarlet is associated with oxygen-rich arterial blood and crimson with deoxygenated venous blood, there is overlap between the two. Cultural associations also give crimson and scarlet symbolic meaning related to passion, sacrifice, adultery, prestige, and more. Understanding normal blood’s red color provides a baseline for identifying abnormalities that may indicate disease.