Bruises are a common physical occurrence resulting from injury or trauma that causes small blood vessels under the skin to rupture.

The intriguing and often striking changes in bruise color reflect a complex biological process where the body breaks down and clears away the leaked blood.

The Initial Stage: Red and Purple Hues

When a bruise first forms, it appears red or reddish-purple because fresh blood escapes the damaged capillaries and pools just beneath the skin. This blood is rich in oxygenated hemoglobin, the molecule that carries oxygen in red blood cells, giving it a bright red appearance.

Within hours or days, as the oxygen is depleted, the injured area darkens to deep purple or blue. This change is largely due to the blood turning deoxygenated, and the blood pooling can also become clotted. This early stage reflects ongoing bleeding and the initial inflammatory response triggered by tissue damage.

Transition Through Blue and Black Shades

The blue and black colors during the next phase of bruise development are caused by the breakdown of hemoglobin into byproducts. As red blood cells degrade, hemoglobin is metabolized into compounds that exhibit different colors. The dark blue-black appearance indicates dense blood accumulation without oxygen.

This stage usually lasts a few days as the body starts to clean up the damaged cells. The intensity of these colors can vary based on the bruise depth, location, and the individual's skin tone.

Green Stage: Biliverdin Formation

As healing progresses, the hemoglobin in the bruised area breaks down further into biliverdin, a green pigment. This pigment is one of the early intermediate products formed during hemoglobin degradation. The development of green hues signals that the body's enzymatic processes are actively converting blood pigments as part of clearing the injury site. The green coloration typically emerges within 5 to 10 days after the initial injury.

It marks the phase where the bruise is starting to fade from the darker colors and the body is metabolizing the trapped blood components efficiently.

Yellow Stage: Bilirubin Presence

Following the green phase, the breakdown products are metabolized further into bilirubin, a yellow pigment. The appearance of yellow in bruises usually occurs between 7 to 14 days post-injury and signifies continued healing. This yellow color indicates residual blood breakdown products being reabsorbed and cleared away by specialized immune cells. During this stage, the inflammation has typically reduced, and tissue repair processes dominate.

Fading to Brown and Resolution

Eventually, the bruise fades to a brownish color due to the presence of hemosiderin, an iron-storage complex formed from degraded hemoglobin components. This rusty brown shade is often the last visible marker before the bruise disappears entirely. The fading process varies in duration but generally concludes within two weeks.

The speed depends on factors such as injury severity, blood flow to the area, and individual metabolic efficiency in clearing pigments.

Biological Processes Behind Color Changes

The dynamic color shifts in bruises are tightly linked to physiological activities involving blood cells and immune responses. After vessel rupture, immune cells rush in to phagocytize or engulf—the damaged red blood cells. These cells break down hemoglobin stepwise, producing biliverdin, then bilirubin, and finally hemosiderin.

These pigments differ chemically and visually, leading to the distinctive color spectrum seen in healing bruises. Enzymes like heme oxygenase are essential for converting hemoglobin to biliverdin, which then undergoes further enzymatic changes.

Clinical Significance and When to Seek Help

The progression of bruise colors provides useful clues about the timing and severity of an injury. For instance, a fresh red or purple bruise suggests recent trauma, while greenish or yellow bruises hint at healing phases.

However, certain bruising patterns—such as bruises that fail to resolve over several weeks, significantly swell, or occur with excessive pain—may warrant medical evaluation. Unexplained large or recurrent bruises could indicate underlying blood clotting disorders or other health issues.

Katherin Scafide, a forensic nurse and bruise scientist, explains "Our classic understanding of that bruise coloration comes from Caucasian skin. So, obviously, a fresh bruise on someone with really dark skin is not going to look red or blue. It's not going to go through the same kind of coloration."

Bruises change color due to the stepwise breakdown of hemoglobin from leaked blood trapped beneath the skin. Starting with fresh red and transitioning through purple, blue, green, yellow, and eventually brown, these stages reflect the body's natural process of clearing damaged blood cells and repairing injured tissues.