Bruises happen when small blood vessels just beneath your skin burst from 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. The process is almost always harmless, but how easily you bruise, how long they last, and what colors they turn all depend on factors worth understanding.
What Happens Under Your Skin
Your body contains a vast network of tiny blood vessels called capillaries running just below the skin’s surface. When you bump into something, those fragile vessels can rupture on impact. Blood spills out into the soft tissue around them and pools there, creating the familiar discoloration.
A standard bruise involves clusters of these small vessels breaking close together, with blood collecting just under the skin. When a larger vessel bursts, typically from a harder hit, the pooling is deeper and more substantial. This creates a hematoma: a raised, painful lump that takes significantly longer to heal, sometimes a month or more. If you feel a firm bump forming inside a bruise, that’s a sign the bleeding went deeper than a surface bruise.
Why Bruises Change Color
The rainbow of colors a bruise cycles through isn’t random. It’s a visible timeline of your body cleaning up the leaked blood, specifically breaking down hemoglobin, the oxygen-carrying molecule inside red blood cells.
When blood first pools under the skin, the bruise looks red or dark purple. Over the next day or two, the trapped red blood cells rupture and release their hemoglobin into the tissue. Your immune cells arrive and begin dismantling the hemoglobin molecule piece by piece. First, the iron-containing core of hemoglobin gets converted into a green pigment, which is why bruises often shift to a greenish hue around days three to five. That green pigment then gets converted into a yellow one, giving older bruises their faded yellowish-brown look. The leftover iron gets stored as a brownish compound, which is why some bruises take on a rusty tinge before they finally disappear.
Most bruises resolve completely within two to three weeks, though deeper ones can linger longer. The entire color sequence, from purple to green to yellow to gone, is simply your body recycling the spilled blood.
Why Some People Bruise More Easily
If you feel like you bruise from the slightest knock, several factors could be at play.
Age. As you get older, the connective tissue in your skin breaks down from years of sun exposure and natural aging. The skin literally thins, and blood vessels underneath become more fragile. 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. These bruises, sometimes called senile purpura, look dramatic but are a normal consequence of aging rather than a sign of disease.
Sex. Women tend to bruise more easily than men, particularly on the upper thighs and arms. This pattern, called purpura simplex or “easy bruising,” is common and usually nothing to worry about.
Medications. Common pain relievers like ibuprofen and aspirin reduce your blood’s ability to clot by interfering with platelet function. Platelets are the cell fragments responsible for plugging damaged vessels, and when they can’t aggregate properly, even minor bumps cause more bleeding under the skin. Blood-thinning medications prescribed for heart conditions have a similar effect. If you’ve started a new medication and noticed more bruising, that connection is likely real.
Nutritional gaps. Vitamin C is essential for building collagen, the structural protein that helps keep blood vessel walls strong. Without enough of it, vessels weaken and break more easily. Vitamin K plays a different but equally important role: your body needs it to form blood clots. Without adequate vitamin K, bleeding from even minor vessel damage takes longer to stop, which means more blood pools under the skin before the leak seals.
How To Help a Bruise Heal Faster
You can’t make a bruise vanish overnight, but you can reduce its severity in the first hours. The Mayo Clinic recommends applying an ice pack wrapped in a thin towel for 20 minutes at a time, repeating several times over the first day or two. The cold constricts blood vessels near the injury, limiting how much blood leaks into the tissue. Less leaked blood means a smaller, lighter bruise.
Elevating the bruised area above heart level, when practical, also helps slow blood flow to the site. After the first 48 hours, gentle warmth can help your body reabsorb the pooled blood more quickly.
When Bruising Signals Something Deeper
Most bruises are unremarkable. You bump your shin on a coffee table, a purple mark shows up, and it fades on its own. But certain patterns of bruising can point to underlying problems with blood clotting or vessel integrity.
Bruises that appear without any trauma you can recall, especially if they’re larger than a centimeter, deserve attention. The same goes for bruising accompanied by frequent nosebleeds (more than five episodes a year, or any that last longer than 10 minutes), or small cuts that keep bleeding for more than five minutes. These patterns can indicate a platelet disorder, a clotting factor deficiency, or another hematological condition that makes bleeding harder to control.
Location matters too. Bruises on the shins and forearms from everyday bumps are normal. Bruises on the trunk, back, or face without a clear cause are less typical and more worth investigating. In children who aren’t yet mobile, any bruising at all is considered unusual, since babies who can’t crawl or walk rarely generate the kind of impact that causes vessel damage.
A bruise that forms a hard, painful lump rather than lying flat under the skin suggests a hematoma, which occasionally needs medical drainage if it’s large enough. And if bruising is severe enough to require a blood transfusion or surgical intervention after a minor injury, that’s a significant indicator of an undiagnosed bleeding disorder.