Why do bruises change color?

The Hook

A fresh bruise is red-purple, then blue, then green, then a sickly yellow-brown before it fades. That rainbow isn’t random — each color is a different chemical stage as your body dismantles the blood that leaked under your skin.

The Science

A bruise starts when a blow breaks tiny blood vessels beneath the skin without breaking the skin itself. Blood leaks into the surrounding tissue and gets trapped. At first it looks red, then purple or blue-black as the trapped blood loses its oxygen (and because it’s being viewed through skin).

Now the cleanup begins. Immune cells move in to recycle the spilled blood’s main pigment, hemoglobin — the molecule that carried oxygen. As they break it down, it passes through a sequence of colored waste products: first biliverdin, which is green, then bilirubin, which is yellow. That’s why an aging bruise turns green, then yellow. Finally the leftovers are carried away and the skin returns to normal.

So the color literally tracks the chemistry: red-blue (fresh trapped blood) → green (biliverdin) → yellow (bilirubin) → gone.

The cleanup crew doing all this is mostly a type of immune cell called the macrophage — literally “big eater.” Macrophages engulf the spilled red blood cells and break their hemoglobin down step by step, which is exactly why the colors appear in a fixed order rather than all at once.

Depth matters too. A bruise deep in muscle has farther to travel and more blood to clear, so it can take weeks; a shallow one under thin skin fades faster. That’s also why the same bump can look dramatically worse on someone whose skin is thin or who bruises easily — the chemistry is identical, but you’re simply seeing more of it.

Three Wild Facts

• Biliverdin, the green stage of a bruise, is the very same pigment that gives some birds’ eggs their blue-green color.
• Bilirubin, the yellow stage, is the exact molecule that turns skin and eyes yellow in jaundice — a bruise is essentially jaundice in miniature.
• Despite the tidy color sequence, doctors can’t precisely date a bruise from its color alone — healing speed varies too much between people and body parts for it to be reliable forensic evidence.

Why It Matters

You’re watching your body’s recycling system in real time — the exact same pigment pathway that, when it backs up in your blood, turns skin and eyes yellow in jaundice. A bruise is a harmless local version of that process.