Every few days I get a bruise bumping into something or another. Still, I can’t help but do the exact same thing every time a new bruise shows up: I follow its progress. What can I say? I’m a dermatologist, I’m weird like that. You should see how excited I am when I get a paper cut!

When you bump into something, a few blood vessels are broken, and blood seeps into the surrounding tissue. Since this is not a “normal” situation, the body reacts quickly by bringing in the troops, or white blood cells, to get rid of this “invasion.” After all, blood belongs inside vessels, not in tissues.

The changing colors of a bruise are a result of this tiny battle.

To understand what happens, we have to take a closer look at hemoglobin. In normal circumstances, old red blood cells get recycled and make way to new healthy ones. A red blood cell lasts about four months, after which it is eliminated by the body, and the hemoglobin in it is broken down into various components, some of which are recycled (like iron) and some of which are eliminated through the intestines and kidneys (like bilirubin).

Follow the numbers: hemoglobin is broken down into heme and globin. Globin is broken down into amino acids, while heme is broken down into iron, biliverdin and bilirbin. In a bruise, all of this happens under the skin, so you see the colors of all the products of breakdown.

Depending on what stage of the hemoglobin breakdown has been reached, the bruise changes its color: First, it’s red: When hemoglobin is still carrying oxygen, its red in color.

Then, its blue or purple: This is the first change of color seen in a bruise. It is simply the result of the hemoglobin losing the oxygen.

Then, it’s green: Hemoglobin is taken up by macrophages (a kind of white blood cells) and are first broken down into biliverdin, which is green.

Then, it’s yellow: Bilirubin is the product of biliverdin breakdown. (Side note: When the levels of bilirubin are high in the blood due to liver disease, the skin turns yellow.)

Then it’s brown: Hemosiderin is a complex present in macrophages, and it stores iron. Iron is one part of the heme protein that is normally recycled by the body to be used in other functions, or to simply make new red blood cells. However, when blood gets trapped under the skin, hemosiderin builds up under the skin temporarily to store all the excess iron.

Then, it’s gone!: Eventually the body gets rid of all the breakdown products of hemoglobin, and the skin returns to looking normal again. Most bruises take about a week or so to heal. However, the deeper and bigger the bruise, the longer it takes to heal, sometimes taking months. If a lot of blood has collected under the skin, or it is in a vital, moving part, a bruise can be associated with considerable pain.

A bruise resolving from the center outwards: the center is almost clear, with some yellow areas, while the periphery are still red/purple

These changes in color can occur simultaneously in a bruise: One part would be at the yellow stage while other parts are still at the purple stage.

IMPORTANT: If bruises keep occurring repeatedly without reason, this might be an indication of medical conditions such as blood disorders, inherited disease, or a mix up in blood thinner. It is necessary to seek medical consultation in such circumstances.

Thank you for reading!

Sources:

KE. Barrett et al. Blood as a Circulatory Fluid and the Dynamics of Blood and Lymph Flow. In: Ganong’s Review of Medical Physiology. 24^th Edition. McGraw-Hill 2012.

K. Reddy, EJ. Lowenstein. Forensics in Dermatology, Part I. Journal of the American Academy of Dermatology 2011; 64 (5): 801-8.

RL. Sham, CW. Francis. Evaluation of mild bleeding disorders and easy bruising. Blood Reviews 1994; 8 (2): 98-104.