A bruise forms when a blow or impact ruptures tiny blood vessels beneath your skin without breaking the skin itself. Blood leaks out of those damaged vessels and pools in the surrounding tissue, creating the familiar discoloration that changes color over roughly two weeks as your body breaks down and reabsorbs the escaped blood.
What Happens Inside Your Skin
Three things need to happen for a bruise to appear. First, enough force has to hit your skin to rupture small blood vessels underneath, but not so much that it tears the skin open. This is why bruises come from blunt impacts like bumping into furniture or getting hit by a ball. Second, blood pressure inside those vessels has to be high enough to push blood out into the surrounding tissue. Third, the bleeding has to occur close enough to the skin’s surface for you to actually see it.
Most of the time, blood pools between the two deepest layers of your skin, where loose connective tissue gives it room to spread. Once blood escapes, your body launches a cleanup response. White blood cells called neutrophils arrive first, followed by macrophages, larger immune cells that engulf and digest the debris. This cellular cleanup crew is responsible for the chemical changes that make your bruise shift color over the following days.
Why Bruises Change Color
The color progression of a bruise is a visible record of your body breaking down hemoglobin, the oxygen-carrying protein inside red blood cells. A fresh bruise looks pinkish or red because intact red blood cells and free hemoglobin are sitting just under the skin. Over the next day or two, as those cells break apart and the hemoglobin loses oxygen, the bruise darkens to deep blue or purple.
From there, enzymes convert the hemoglobin into intermediate compounds that shift the color to brown, then green, then dark yellow, and finally a pale yellow before fading entirely. The green and yellow stages come from byproducts your body produces as it recycles the iron and protein from the spilled blood. A typical bruise runs through this entire sequence and disappears within about two weeks.
Flat Bruises vs. Raised Hematomas
Not all bruises look or feel the same. A standard bruise is flat, spreading out in a thin layer through the tissue. It can be tender but usually isn’t swollen. A hematoma, on the other hand, involves a larger volume of blood collecting in one spot, creating a raised, firm lump that’s painful to touch. Hematomas typically result from more significant trauma, like a hard fall or car accident, and may need medical attention if they’re large or don’t resolve on their own.
A quick way to tell them apart: if the discolored area is flat, it’s a standard bruise. If it’s noticeably swollen or raised, it’s likely a hematoma.
Bone Bruises Feel Different
Bones can bruise too. A bone bruise happens when an impact is hard enough to cause bleeding inside the bone itself, but not hard enough to cause a fracture. It takes considerably more force than a skin bruise, and the sensation is different: a deep, throbbing ache that feels like it’s coming from inside your body rather than the surface.
Because bone bruises are so deep, you often can’t see any skin discoloration at all. They also heal much more slowly. While a skin bruise clears up in about two weeks, bone bruises last several weeks at minimum, and more severe ones can take months.
Why Some People Bruise More Easily
Aging is one of the biggest factors. As skin matures, it loses collagen and subcutaneous fat, both of which normally cushion and support the tiny blood vessels running through it. Without that structural support, even minor bumps can rupture vessels and cause bruising. The junction between skin layers also flattens with age, making the tissue less resilient overall. This is why older adults often develop bruises on their forearms and hands from contact that wouldn’t leave a mark on younger skin.
Vitamin C plays a direct role in keeping blood vessels strong. Your body needs it to build collagen, the protein that reinforces capillary walls. When vitamin C levels drop too low, those walls weaken and break down, leading to increased bleeding and bruising even without significant trauma. This is the same mechanism behind scurvy, though you don’t need to be that deficient to notice easier bruising.
Several common medications also increase bruising risk. Blood thinners reduce your blood’s ability to clot, so even small vessel ruptures bleed more freely into surrounding tissue. NSAIDs like aspirin and ibuprofen have a similar effect. Steroids like prednisone thin the skin over time, making vessels more vulnerable. Even combining a daily aspirin with another anti-inflammatory can noticeably increase how often and how easily you bruise.
Reducing a Bruise After Impact
If you act quickly after an injury, you can limit how much blood leaks into the tissue and reduce the size of the bruise. Ice is the most effective tool, but timing matters. It works best within the first eight hours after the injury. Apply it with a thin barrier (a cloth or towel) between the ice and your skin, and keep it on for 10 to 20 minutes at a time, repeating every hour or two. The cold constricts blood vessels, slowing the flow of blood into the damaged area.
Elevating the bruised area above your heart, when possible, also helps by reducing blood pressure at the injury site. Compression with a snug bandage can limit swelling, especially with deeper bruises. After the first day or two, gentle warmth can help your body reabsorb the pooled blood faster.
When Bruising Signals Something Else
Occasional bruises from known bumps and impacts are completely normal. What warrants attention is a pattern of bruising that doesn’t match any injury you remember, bruises that are unusually large, or bruising that appears in uncommon locations like your torso or back. These patterns can point to underlying conditions that affect how your blood clots, including liver disease, certain cancers like leukemia, or inherited bleeding disorders like hemophilia. Autoimmune conditions that lower your platelet count can also cause unexplained bruising, since platelets are the first responders that plug damaged blood vessels and stop bleeding.