Bruises form when small blood vessels just beneath your skin burst from an impact and leak blood into the surrounding tissue. That trapped blood, visible through your skin as a dark mark, is what you’re actually seeing when you notice a bruise. Most bruises heal completely within about two weeks, but the process your body uses to clean up that leaked blood is surprisingly complex and explains the rainbow of colors a bruise cycles through before it disappears.
What Happens Under Your Skin
When you bump into something hard enough, the force travels through your skin and crushes tiny blood vessels called capillaries. These vessels are incredibly thin, and even moderate pressure can rupture them. Once they break, blood spills into the soft tissue around them and pools just below the skin’s surface. Your body registers this as damage and immediately starts sending repair signals to the area.
The size of a bruise depends on how many vessels broke and how much blood leaked out. A minor bump might rupture a handful of capillaries, producing a small, faint mark. A harder impact can damage larger vessels deeper in the tissue, creating a hematoma, which is a bigger, more swollen collection of pooled blood. That’s why a bruise from walking into a coffee table looks and feels different from one caused by a serious fall.
Why Bruises Change Color
The color shift from dark purple to green to yellow isn’t random. It tracks a specific chemical process happening inside the bruise as your body breaks down the trapped blood.
Red blood cells caught outside your blood vessels eventually rupture, releasing hemoglobin, the protein that gives blood its red color. Immune cells called macrophages move in to digest this hemoglobin, breaking it into smaller components in a predictable sequence. First, the heme portion of hemoglobin converts into a green pigment called biliverdin, which is why bruises develop that greenish tint after a few days. Then biliverdin converts into bilirubin, a yellow pigment, explaining the yellowish phase near the end of healing. Meanwhile, iron left over from the hemoglobin gets stored as hemosiderin, a brownish compound, which accounts for the brownish discoloration some bruises develop.
A fresh bruise looks red or purplish because you’re seeing intact hemoglobin through the skin. Over the next several days, as each chemical conversion happens, the bruise shifts through blue, green, yellow, and brown before fading entirely. The whole cycle typically wraps up in about two weeks for a standard bruise, though deeper or more severe ones can linger longer.
Why Some People Bruise More Easily
If you feel like you bruise from barely anything, you’re not imagining it. Several factors make some people’s blood vessels more vulnerable than others.
Age: As you get older, your skin literally thins. Ultrasound measurements show that atrophic (thinned) skin measures roughly 0.7 to 0.8 millimeters thick, compared to about 1.4 to 1.5 millimeters for normal skin. That’s nearly half the protective cushion gone. The fatty layer beneath the skin also shrinks with age, removing another buffer that once absorbed impacts before they reached blood vessels. This is why older adults often develop dark bruises on their forearms and hands from contact that wouldn’t leave a mark on younger skin. In one study of patients 65 and older, researchers found that a dermal thickness below 0.80 millimeters was a significant predictor of skin tears and easy bruising.
Sex: Women tend to bruise more easily than men, particularly on the upper arms and thighs. This pattern is common enough to have its own clinical name (purpura simplex) and is considered a normal variation rather than a sign of disease.
Nutritional gaps: Vitamin C plays a direct role in building collagen, the structural protein that helps keep blood vessel walls strong. Without enough of it, vessels become fragile and break more easily. Vitamin K is essential for blood clotting. Your body needs it to form the clots that stop bleeding after a vessel breaks. When vitamin K levels are low, even small amounts of leaked blood take longer to contain, and bruises become more prominent.
Medications That Increase Bruising
Several common medications reduce your blood’s ability to clot, which means more blood escapes when a vessel breaks and bruises show up faster and larger. Blood thinners are the most obvious culprit, but they’re far from the only one. NSAIDs like aspirin and ibuprofen interfere with platelet function, making it harder for your body to plug damaged vessels quickly. Taking an NSAID alongside a blood thinner compounds the effect. Corticosteroids like prednisone thin the skin over time, reducing its ability to protect underlying vessels. Chemotherapy drugs can also lower platelet counts, leading to easier bruising during treatment.
If you’ve started a new medication and notice more bruising than usual, that connection is worth flagging with your prescriber. It doesn’t necessarily mean the drug needs to change, but it helps explain what you’re seeing.
Bone Bruises Are Different
Not all bruises are visible. A bone bruise, or bone contusion, happens when blood becomes trapped beneath the surface of a bone after an impact. The healing stages are similar to a skin bruise, but you can’t see any color changes because the damage is deep inside your body. What you feel instead is persistent, aching pain at the injury site.
Bone bruises also heal much more slowly. While a typical skin bruise resolves in two weeks, bone bruises can take months or longer to fully recover. The key difference is that a bone bruise leaves a weak spot in the bone. If you return to intense activity before it heals, that weakened area has a higher risk of progressing to a full fracture. Skin bruises are hard to make worse, but bone bruises require real rest.
When Bruising Signals Something Deeper
Occasional bruises from bumps and falls are completely normal. The bruising that warrants attention looks different: it appears without any injury you can recall, shows up in unusual locations, or comes alongside other signs of bleeding like frequent nosebleeds, bleeding gums, or blood in your urine.
Clinicians distinguish between two broad patterns. Bruising that appears alongside tiny pinpoint dots on the skin, nosebleeds, or gum bleeding typically points toward a problem with platelets, the cell fragments responsible for initial clot formation. The most common platelet-related bleeding disorder is von Willebrand disease. Bruising that occurs with deep muscle bleeding or joint swelling suggests a different category of problem involving the clotting proteins themselves, as seen in hemophilia.
A few specific patterns raise concern. Bruises in children who aren’t yet mobile enough to injure themselves, bruises shaped like objects, or bruises in locations inconsistent with the reported injury can indicate physical abuse. In older adults, large dark bruises concentrated on the forearms, particularly over the backs of the hands and arms, are characteristic of age-related skin fragility rather than a blood disorder.
Unexplained bruising combined with an enlarged liver can suggest liver failure, since the liver produces many of the proteins your blood needs to clot. Unexplained bruising with an enlarged spleen may point toward an underlying blood cancer. These are uncommon causes, but they illustrate why persistent, unexplained bruising sometimes warrants blood work to check clotting function and platelet counts.