Why and how do bruises change colour?
Bruises change colour as the body heals the damaged tissue. The colour changes occur because of the breakdown of haemoglobin, the oxygen-carrying protein in red blood cells.
When blood vessels are damaged, haemoglobin leaks out of the cells and into the surrounding tissue. This causes the tissue to appear red or purple, which is the colour of haemoglobin.
Over time, the body starts to break down the haemoglobin and remove the damaged tissue. As this happens, the colour of the bruise changes from red to blue, green, yellow, and finally brown. This is because the breakdown products of haemoglobin have different colours.
The following is a more detailed explanation of the colour changes that occur during the healing process:
* Red: The initial colour of a bruise is red because of the presence of haemoglobin. Haemoglobin is the oxygen-carrying protein in red blood cells, and it gives blood its red colour.
* Blue: As the body starts to break down haemoglobin, the bruise turns blue. This is because the breakdown products of haemoglobin, called biliverdin and bilirubin, are blue-green in colour.
* Green: The bruise then turns green because the biliverdin is converted to bilirubin. Bilirubin is a yellow-brown pigment that is also found in urine and faeces.
* Yellow: The bruise eventually turns yellow because the bilirubin is broken down into other compounds that are yellow in colour.
* Brown: The final colour of a bruise is brown because of the presence of hemosiderin. Hemosiderin is a compound that contains iron, and it is formed when haemoglobin is broken down.
How do bruises change colour?
The colour changes of a bruise are caused by the body's natural healing process. As the body breaks down haemoglobin and removes the damaged tissue, the colour of the bruise changes. The following is a more detailed explanation of the processes that cause these colour changes:
* Red blood cell damage: When blood vessels are damaged, red blood cells leak out into the surrounding tissue. This causes the tissue to appear red because of the presence of haemoglobin.
* Haemoglobin breakdown: The body starts to break down haemoglobin into biliverdin and bilirubin. Biliverdin is blue-green in colour, while bilirubin is yellow-brown.
* Biliverdin and bilirubin removal: Biliverdin and bilirubin are transported by the blood to the liver. The liver breaks down biliverdin and bilirubin into other compounds that are excreted in urine and faeces.
* Hemosiderin deposition: Some of the iron from haemoglobin is stored in the form of hemosiderin. Hemosiderin is a brown pigment that gives bruises their final colour.
Factors that affect how long a bruise takes to heal
The following factors can affect how long a bruise takes to heal:
* The severity of the injury: More severe injuries will cause more extensive damage to the tissue and will take longer to heal.
* The location of the injury: Bruises on the face and legs tend to heal more slowly than bruises on other parts of the body.
* Age: Bruises tend to heal more slowly as we age.
* Certain medical conditions: Some medical conditions, such as diabetes, can slow down the healing process.