A bruise is a pool of leaked blood trapped beneath your skin’s surface. What you see on the outside, that familiar dark patch, is actually blood that has escaped from damaged blood vessels and collected in the soft tissue underneath. The appearance changes over time as your body breaks down that trapped blood, shifting through a predictable sequence of colors over roughly two weeks.
What Happens When a Bruise Forms
When something hits you hard enough to damage tissue but not break the skin, small blood vessels just below the surface burst open. Blood leaks out of those vessels and seeps into the surrounding tissue, filling the tiny spaces between cells in your skin, fat layer, or muscle. This pooled blood is what creates the visible discoloration you recognize as a bruise.
The size of the bruise depends on how many blood vessels were damaged and how large they were. A minor bump might rupture a few tiny capillaries, producing a small, faint mark. A harder impact can burst larger vessels, creating a bigger pool of blood that spreads out under the skin. In some cases, the blood collects into a distinct lump called a hematoma, which you can actually feel as a raised, firm area beneath the surface.
The Color Stages of a Bruise
The changing colors of a bruise aren’t random. They reflect a chemical process happening underneath your skin as your body dismantles the trapped red blood cells and recycles their components. A bruise typically resolves completely within about two weeks, and each color stage marks a different phase of that cleanup.
In the first hours after injury, the bruise appears pinkish or red. This is fresh, oxygen-rich blood sitting close to the skin’s surface. Within a day or two, the bruise deepens to a dark blue or purple as the blood loses oxygen and the red pigment in your blood cells begins to break down.
Over the next several days, the bruise shifts to a violet or greenish tone. This green color comes from a breakdown product of the blood’s red pigment, created when enzymes in your tissue start processing the trapped blood. After that, the green gives way to dark yellow and then pale yellow as a second chemical conversion takes place. The leftover iron from the blood gets stored as a brownish compound, which is why some bruises take on a brownish-yellow tinge in their final days before fading completely.
Not every bruise follows this sequence neatly. A large bruise might show several colors at once, with the edges healing faster than the center. The outer rim could look yellowish-green while the middle is still deep purple.
How Deep Bruises Differ From Surface Ones
A bruise sitting just beneath the top layer of skin shows up quickly and displays vivid colors. But bruises can also form much deeper, in muscle tissue or even against bone, and these look and feel quite different on the surface.
Deep muscle bruises happen when a blow compresses soft tissue against the underlying bone, crushing muscle fibers and blood vessels in between. These injuries produce swelling and stiffness that surface bruises don’t. A mild deep bruise might cause only slight soreness when you press on it. A moderate one can limit your range of motion and cause a limp. Severe muscle bruises are painful, noticeably swollen, and produce obvious surface discoloration, but that discoloration can take longer to appear because the blood has to migrate upward through layers of tissue before it becomes visible.
This delay is why you sometimes notice a bruise appearing a day or two after an injury in a spot slightly away from where the actual impact occurred. Blood pools at the depth of the injury, then gradually tracks along tissue planes toward the surface, sometimes settling in a lower area due to gravity.
What a Bruise Looks Like on Imaging
When doctors need to see what’s happening beneath a bruise, ultrasound can reveal the actual dimensions of the blood pool under the skin. Research published in Forensic Science International found that ultrasound could objectively measure the subcutaneous size of a bruise, showing that the blood collection beneath the surface doesn’t always match what’s visible on the outside. The bruise you see may be smaller or larger than the actual pocket of blood underneath.
Interestingly, bruises that are more than 48 hours old may not show up on ultrasound at all, because the body has already begun reabsorbing the pooled blood. More severe injuries involving deeper muscle damage sometimes require a high-frequency ultrasound probe to visualize the hematoma within the muscle itself.
Why Some People Bruise More Easily
The same impact can leave a large, dark bruise on one person and barely a mark on another. Several factors influence how easily bruises form and how dramatic they look.
Aging plays a major role. As you get older, your skin thins and loses the protective fatty layer that normally cushions blood vessels from impact. That means less force is needed to rupture those vessels, and the resulting bruise is often more visible through the thinner skin above it.
Medications that reduce your blood’s ability to clot, including aspirin and ibuprofen, allow more blood to leak out before the damaged vessels seal themselves. The longer the bleeding continues under the skin, the larger the bruise becomes. Corticosteroids thin the skin itself, making bruising easier for a different reason. Even some dietary supplements like ginkgo biloba have a mild blood-thinning effect that can increase bruising.
If you’re bruising frequently without clear injuries, or if bruises are unusually large or slow to heal, that can signal a problem with your blood’s clotting system. Low platelet counts, platelet function disorders, or problems with clotting proteins can all cause excessive bruising. These conditions affect how quickly your body stops the bleeding after a vessel breaks, allowing larger pools of blood to accumulate under the skin.
Normal Bruises vs. Concerning Signs
A typical bruise from a known bump or fall follows the color progression described above and fades within about two weeks. It might be tender to touch for the first few days but shouldn’t cause severe pain or significant swelling.
Bruises that raise concern tend to share certain features: they appear without any injury you can remember, they’re unusually large relative to the impact, they keep appearing in new locations, or they take much longer than two weeks to resolve. A bruise accompanied by a firm, growing lump could indicate a larger hematoma that isn’t reabsorbing normally. Bruises that appear around the eyes or behind the ears after a head injury can indicate bleeding at a deeper level and need prompt evaluation.
The location matters too. Bruises on the shins and forearms are common and usually harmless, since those areas bump into things frequently. Bruises on the torso, back, or face without a clear cause deserve more attention, particularly in children or elderly adults.