Why Do Bruises Change Color as They Heal?

A bruise can pass through shades of red, purple, blue, green, and yellow without anything new entering the skin. The changing colors reveal the body dismantling blood that escaped from damaged vessels.

A blow can rupture tiny blood vessels without breaking the skin. Blood leaks into the surrounding tissue, where red blood cells and hemoglobin begin producing the bruise's early reddish or dark purple appearance.

The exact color depends on depth, oxygen levels, lighting, skin pigmentation, and the severity of the injury. A bruise may appear blue even though the blood itself is not blue because skin and tissue alter the light returning to the eye.

The body gradually sends immune cells into the damaged area. These cells collect and break down the escaped red blood cells. Hemoglobin is separated into other compounds during this cleanup.

One product is biliverdin, a pigment with a green color. Biliverdin is then converted into bilirubin, which appears yellow or yellow brown. Iron from the hemoglobin can be stored temporarily in compounds such as hemosiderin, sometimes contributing brown tones.

The pigments do not always appear in a perfectly ordered sequence. Different portions of the same bruise may be at different stages, and color alone cannot determine its exact age reliably.

Eventually, the breakdown products are removed or recycled, the damaged vessels are repaired, and the normal skin color returns.

A healing bruise is therefore a temporary display of blood recycling. Its colors change because a single red pigment is being dismantled into a succession of chemically different materials before the body carries them away.