Bruises turn purple because blood leaking from damaged vessels loses oxygen once it’s trapped in your tissue. Fresh blood is red, but deoxygenated hemoglobin absorbs light differently, shifting the color toward a dark purple or blue. The depth of the bruise also plays a role: your skin itself filters the light passing through it, scattering blue wavelengths back to your eyes more than red ones.
What Happens Under Your Skin
When you bump into something hard enough to break tiny blood vessels (but not the skin itself), blood spills into the surrounding tissue. Red blood cells pile up in a space they don’t belong, and without a continuous supply of fresh oxygen from your bloodstream, their hemoglobin changes shape. That molecular shift is what changes the color you see on the surface.
Hemoglobin is the protein inside red blood cells that carries oxygen. When it’s loaded with oxygen, it reflects red light. Once it releases that oxygen, it absorbs red light instead and reflects shorter wavelengths, producing a dark purplish-blue tone. This is the same reason veins on your wrist look blue even though the blood inside them is actually a deep maroon. Your skin acts as a filter, and the physics of light scattering through tissue amplifies the blue end of the spectrum.
Why Deeper Bruises Look Bluer
Not all bruises look the same shade of purple, and the depth of the injury is a big reason why. A bruise sitting close to the skin’s surface tends to look more red or reddish-purple because less tissue is filtering the light between the pooled blood and your eyes. A bruise buried deeper in fat or muscle appears more blue or even indigo. This happens because of a process called Rayleigh scattering: as light passes through the layers of your skin, shorter (bluer) wavelengths bounce around and get reflected back more than longer (redder) wavelengths. The more tissue the light has to travel through, the stronger this blue-shifting effect becomes.
This is also why the same bruise can look different on different people. Skin tone, skin thickness, and the amount of fat between the injury and the surface all affect which wavelengths reach your eyes.
How Your Body Clears a Bruise
Your immune system treats trapped blood like debris that needs to be cleaned up. White blood cells called macrophages arrive at the injury site and start engulfing the red blood cells and their contents. They break hemoglobin apart into its components: a protein portion and a pigmented molecule called heme, which contains iron. An enzyme inside the macrophages then splits heme into three things: iron atoms (which get recycled), carbon monoxide (which gets exhaled), and a green pigment called biliverdin.
Biliverdin is quickly converted into bilirubin, a yellow pigment. Meanwhile, some of the leftover iron gets stored in a brownish compound called hemosiderin. These chemical changes are the reason a bruise doesn’t just stay purple. It cycles through a predictable series of colors as each pigment is produced and then cleared away.
The Color Timeline
A bruise follows a rough schedule, though the timing varies depending on severity and location:
- Day 1: Red to dark purple. Fresh, deoxygenated blood pools under the skin.
- Days 2 to 3: Deep purple to blue-black. Hemoglobin continues to lose oxygen and macrophages begin arriving in force.
- Days 4 to 5: Green tones appear. Biliverdin production peaks around this window as macrophages actively break down heme.
- Days 5 to 10: Yellow and brown. Bilirubin and hemosiderin dominate as the breakdown products are gradually absorbed.
- Days 10 to 14: Fading to skin color. In healthy people, most bruises resolve completely within two weeks.
These stages often overlap. You might see a bruise that’s yellow at the edges (where healing started first) and still purple in the center. That’s because the edges of the bruise have less pooled blood, so macrophages clear it faster.
Why Some Bruises Look Worse Than Others
Several factors affect how vivid and long-lasting a bruise appears. Harder impacts break more vessels, producing a larger pool of blood and a more dramatic purple. Areas with thinner skin, like the forearms, shins, and the tissue around your eyes, bruise more visibly because there’s less tissue masking the color.
Age plays a significant role. As you get older, your skin thins and the small blood vessels beneath it become more fragile. The supportive tissue around those vessels also weakens, meaning less force is needed to cause a bruise, and the resulting discoloration tends to spread more widely. Blood-thinning medications and even common supplements like fish oil can have the same effect by slowing the clotting that would normally limit how much blood escapes.
Bruises That Deserve Attention
Most bruises are harmless and heal on their own. But certain patterns can signal a problem with how your blood clots. Bruises that appear without any injury you can remember are worth paying attention to, particularly if they’re larger than about 3 centimeters (roughly the size of a quarter). Spontaneous bruising at that size, especially if you haven’t taken aspirin or similar medications recently, is considered clinically significant.
Other red flags include bruising that shows up in unusual locations like the neck, buttocks, or around joints, bruising from two or more separate sites at the same time, or bruises that keep getting worse instead of progressing through the normal color cycle. A bruise that hasn’t improved at all after two weeks may also point to an underlying condition affecting your blood’s ability to clot properly.