What do the colors of a bruise mean?

Bruises on our skin mostly occur due to the leakage of blood from the fine blood vessels damaged by trauma into the tissues. If the trauma causes damage to the skin and blood to come out, bleeding occurs.

The area damaged in a trauma is at first red and the rash is caused by blood leaking between the tissues. It gives blood its red color to hemoglobin, which is responsible for transporting oxygen to tissues. When oxygen is attached to the hemoglobin molecule, its color is bright red. When oxygen is not connected, it is blue-purple. For this reason, as the blood loses oxygen, the redness in the damaged part of the skin becomes darker and turns purple.

The color change that occurs during the healing of the bruises results from the changes that hemoglobin has undergone biochemically. Biliverdin is greenish from molecules formed by the breakdown of hemoglobin by macrophage cells. Biliverdin then turns into a yellow bilirubin molecule. Therefore, the color of the bruises changes from purple to green during the healing process and then to yellow. Approximately two weeks after trauma, all of the breakdown products of hemoglobin disappear.