Bruises turn purple because blood leaking from damaged blood vessels loses its oxygen once it’s trapped beneath your skin. When you bump into something hard enough to rupture tiny blood vessels called capillaries, blood escapes into the surrounding tissue. That pooled blood, now cut off from fresh oxygen, shifts from bright red to a dark bluish-purple visible through the skin.
What Happens Inside Your Skin
A bruise starts the moment an impact ruptures small blood vessels just below your skin’s surface. The blood that spills out has nowhere to go, so it pools in the soft tissue around the injury. This is different from a cut, where blood escapes outward. With a bruise, everything stays sealed beneath the skin, and your body has to clean it up from the inside.
The size and depth of a bruise depends on how much force was involved. A small bump might burst a few capillaries, producing a mark that looks like scattered red or purple dots. A harder hit can rupture larger vessels, creating a broad patch of pooled blood that spreads out under the skin. When the pooling is significant, it’s called a hematoma, essentially a deeper, more concentrated collection of trapped blood.
Why the Color Turns Purple
The color comes down to hemoglobin, the protein in red blood cells that carries oxygen. In your arteries, red blood cells carry a full supply of oxygen and appear bright red, which is why healthy skin has a pinkish tone. Once blood leaks out of a vessel and sits in tissue, those red blood cells quickly burn through their remaining oxygen. Deoxygenated hemoglobin is a much darker pigment, a deep bluish-red that looks purple or blue when viewed through layers of skin.
Your skin itself acts as a filter. Light passing through the outer layers of skin shifts how you perceive the color of the blood underneath. The combination of dark deoxygenated blood and the light-scattering properties of skin tissue produces that characteristic purple or blue-black appearance most people associate with a fresh bruise.
How a Bruise Changes Color as It Heals
The purple phase is just the beginning. Over the next two weeks or so, your body breaks down the trapped hemoglobin through a series of chemical steps, and each step produces a different pigment. A typical bruise moves through this progression:
- Red to pink (first hours): Fresh blood is still oxygenated, so the bruise may initially look red or pinkish at the surface.
- Dark blue or purple (days 1 to 3): Oxygen depletes, and the pooled hemoglobin darkens.
- Green (days 5 to 7): Your body uses an enzyme called heme oxygenase to break down the hemoglobin’s core structure into a green pigment. This is why bruises often develop a greenish tint around the edges first.
- Yellow to brown (days 7 to 14): A second enzyme converts the green pigment into a yellow one. The bruise fades from a muddy yellow-brown to pale yellow before disappearing entirely.
Most bruises heal completely within two weeks. Larger or deeper bruises can take longer, and bruises on your legs tend to linger because gravity pulls fluid downward, slowing the cleanup process.
Why Some People Bruise More Easily
Not everyone gets the same bruise from the same bump. Several factors affect how fragile your blood vessels are and how visible the resulting bruise becomes.
Age is one of the biggest factors. As you get older, your skin thins and loses some of its protective fatty layer. Sun exposure accelerates this process. Thinner skin means less cushioning between the surface and your blood vessels, so even minor contact can cause a bruise, and the discoloration shows up more vividly.
Certain medications also increase bruising. Aspirin, ibuprofen, naproxen, and prescription blood thinners all interfere with your blood’s ability to clot, which means more blood escapes from a damaged vessel before the leak seals itself. Long-term use of corticosteroids can weaken both the skin and the blood vessels within it, making bruising more frequent even without obvious trauma. If you’re taking any of these and noticing more bruises than usual, that’s a known side effect rather than a sign of a separate problem.
Fair skin doesn’t bruise more easily, but bruises are more visible on lighter skin simply because there’s less pigment masking the color change underneath.
When a Bruise Signals Something Deeper
Ordinary bruises from identifiable bumps or falls are rarely a concern. But certain patterns are worth paying attention to. A bruise that hasn’t healed within two weeks, frequent bruising with no clear cause, or bruising accompanied by muscle weakness, tingling, numbness, or changes in skin color from poor circulation can all point to underlying issues with blood clotting or vascular health.
A bruise that feels hard, grows rapidly, or causes intense pain may be a hematoma large enough to need medical evaluation. In rare cases, a large hematoma can compress nearby nerves or restrict blood flow, which is why swelling and unusual pain in the area shouldn’t be dismissed if they worsen rather than improve over the first few days.