Why Bruises Change Colour As They Heal

A bruise that starts deep purple and ends a muddy yellow is not fading in the ordinary sense. It is being dismantled chemically, and each stage of the dismantling has its own colour.

A bruise is blood outside a vessel

Blunt force can tear small vessels beneath intact skin. Blood leaks into the surrounding tissue, where it has no route back into circulation and must be cleared where it lies.

The initial red or purple is haemoglobin, the oxygen-carrying pigment inside red blood cells, seen through several layers of tissue. Depth matters, which is why deep bruises look duller.

Swelling and tenderness come from the same event. Fluid and immune cells arrive at the site, and the pressure they create is a large part of what makes a bruise sore to press.

The colour sequence tracks a chemical breakdown

Immune cells called macrophages engulf the escaped red cells and break haemoglobin apart. The molecule does not vanish in one step; it passes through intermediates that each absorb different wavelengths.

Biliverdin comes first and is green. It is converted to bilirubin, which is yellow-brown, and that pigment is eventually carried away and processed by the liver like any other.

So the familiar purple-green-yellow order is not decoration. It is a chemical sequence being read through the skin, which is why the order rarely varies even when the timing does.

Why some people bruise more readily

Vessel fragility and the amount of padding over them both matter. Thinner skin and less subcutaneous fat mean the same knock transmits more force directly to small vessels.

Age changes this steadily. Supporting tissue around vessels becomes less resilient over the decades, which is why older forearms and hands mark from contact that would once have left nothing.

Medicines that affect clotting or platelet behaviour also raise the likelihood. That is a mechanism, not a fault, and it is one reason clinicians ask about medication when bruising changes.

Where the bruise sits changes what you see

Gravity moves pooled blood. A bruise from an injury to the thigh can appear lower down the leg days later, which regularly confuses people about where they were actually hit.

Loose tissue disperses blood widely and tight tissue confines it. Around the eye, where the tissue is loose, a modest injury produces dramatic discolouration out of proportion to the force.

Timing varies with all of this too. Deep bruises may not surface for a day or more, so the absence of an immediate mark says little about severity.

When bruising is worth a clinician's attention

Bruises that appear without remembered injury, appear in unusual places, or arrive alongside bleeding gums or frequent nosebleeds are worth describing to a doctor rather than watching.

The same applies to a bruise that keeps enlarging, becomes hard and hot, or sits over a joint that will not take weight. Those point to something beyond a broken capillary.

A single ordinary bruise on a shin is not a diagnostic event. A pattern is, and pattern is the thing a clinician is actually assessing when they ask how often it happens.