Discoloration of Blood: An Insight into its Causes and Implications

Shivendra Pratap Singh


High Court Lucknow

Medico Legal

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Published on: 13 Aug, 2023

The color of our blood is a captivating indicator of oxygen levels and, more broadly, our overall health. Typically a rich red, changes in the hue of blood can raise eyebrows and concerns. This comprehensive exploration will help elucidate why blood might appear differently and what these variations may signify.

1. The Science of Blood Color

Blood color primarily results from hemoglobin, a protein responsible for carrying oxygen.

  • Oxygen-rich blood: Appears bright red due to oxyhemoglobin.
  • Oxygen-poor blood: Appears darker due to deoxyhemoglobin.

2. Variations in Blood Color:

a. Bright Red Blood: Indicates oxygen-rich blood. This is typically seen in arterial blood, such as that spurting from a cut on the wrist.

b. Dark Red or Maroon Blood: Signifies oxygen-depleted blood. Venous blood, which returns to the heart after delivering oxygen to tissues, presents this hue.

c. Blue or Purple Hue: Sometimes veins might appear blue through the skin, but this isn’t the actual color of the blood. It’s an optical illusion due to skin tone, depth of the veins, and the way light interacts with the skin.

3. Unusual Blood Colors and Their Causes:

a. Brown or Dark Red: Old blood that may be seen at the end of a period or with certain digestive problems.

b. Cherry Red: Presence of carbon monoxide. Hemoglobin binds more readily to carbon monoxide than to oxygen, forming carboxyhemoglobin. This gives blood a bright cherry-red appearance, and it’s a warning sign of carbon monoxide poisoning.

c. Green or Green-Black: A rare condition called sulfhemoglobinemia can turn the blood green. It’s caused by the buildup of sulfur in the blood, often due to certain medications or specific types of food.

4. Clinical Implications of Blood Color Changes:

a. Digestive Health: The color of blood in stool can hint at where bleeding might be occurring in the digestive tract. Bright red blood suggests active or recent bleeding, potentially from hemorrhoids or anal fissures. Darker blood can suggest bleeding further up the digestive tract.

b. Respiratory Health: Cherry red blood may be a sign of carbon monoxide poisoning, and immediate medical attention is required.

c. Methemoglobinemia: A condition where the iron in blood changes form and cannot effectively carry oxygen, leading to a bluish appearance.

5. Addressing Discoloration Concerns:

  • Seek Medical Advice: Anytime there’s an unexpected change in the appearance of your blood, it’s wise to consult a healthcare professional.
  • Monitor Symptoms: If you notice other symptoms accompanying the change in blood color, like shortness of breath, dizziness, or fatigue, seek medical attention promptly.


The color of our blood is more than just a hue; it’s a vivid, visual representation of our internal health. While many factors can affect the color of blood, understanding what each shade signifies can provide critical insights into our well-being. Observing and seeking clarity on any changes can be vital in ensuring optimum health and prompt treatment when necessary.


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