Experts explain that the color of a bruise evolves as blood pools beneath the skin and the components of blood break down. The color shift is a visible clue about what happens in the damaged tissue after an injury and how the body clears the blood that has leaked out of vessels.
A bruise forms when tiny blood vessels under the skin rupture and blood collects in the surrounding soft tissue. At first, the lumped blood appears reddish because fresh blood has a bright red appearance from the oxygen-rich hemoglobin in red blood cells. As time passes, the bruise often shifts to bluish-purple and then to greenish-yellow tones. These color changes are not random; they reflect a sequence of chemical changes in the blood that follow the injury.
Hemoglobin, the protein inside red blood cells that carries oxygen, is responsible for the bruise colors. While red blood cells are circulating, hemoglobin is red when it carries oxygen. When it binds carbon dioxide or loses oxygen, its color can appear different. In a bruise, the blood that escapes from vessels loses oxygen and accumulates carbon dioxide as the body processes it. This initiates a breakdown where hemoglobin transforms through several stages, first into a dark brown pigment called methemoglobin, and then into yellow pigments known as biliverdin and bilirubin. The progression from red to blue or purple to greenish-yellow is a visual cue that these breakdown products are forming and fading as the body reabsorbs the blood. The exact hue seen depends on how quickly the body metabolizes these compounds and on factors like skin tone and the bruise’s location, making each bruise slightly unique in its coloration.
As the damaged area heals, enzymes break down the trapped blood compounds and the body gradually reabsorbs them. The color shifts are typically most noticeable in the first one to two weeks after the injury, though the timeline can vary with age, health, and the severity of the trauma. Persistent swelling, unusual pain, or a bruise that does not begin to fade after several days may warrant medical attention, as these could indicate a more significant injury or an underlying health issue. Clinicians often use the color timeline as a rough guide to estimate when the injury occurred, along with other signs and the patient’s description of events.
Historically, clinicians have noted the most common injuries around particular holiday periods and gatherings, reminding readers that the body’s healing signals, like bruise coloration, can offer practical clues about recent bumps and falls during celebrations.