Why Do Bruises Change Colour?

One minute it is red, the next it is purple and a few days later it has developed a suspicious greenish-yellow glow.

Bruises can look quite scary for something that is usually part of the body’s normal healing process. But those changing colours are not random. They are created as the body gradually clears blood that has leaked into the tissues.

What actually causes a bruise?

A bruise forms when small blood vessels beneath the skin are damaged, often after a bump, fall or other minor injury.

The skin itself may remain intact, but blood escapes from the damaged vessels and collects in the surrounding tissues. This is why a bruise can feel sore or tender before much discolouration is visible. In other words, it is essentially a small amount of bleeding beneath the skin, not blood that has somehow become “stuck” inside a vein.

"NHS guidance", also notes that bruises may not appear immediately after an injury.

Why does the colour change?

Red blood cells contain haemoglobin, the protein responsible for carrying oxygen around the body.

Once blood has leaked into the tissues, the body begins its clean-up operation. Immune cells called macrophages help remove the damaged red blood cells, while haemoglobin and its haem component are broken down into different pigments.

Each pigment reflects light differently, creating the familiar changing appearance of a bruise.

• Red, pink or purple

A newer bruise may initially appear red, pink, purple, blue or very dark.

This early colour comes mainly from blood and haemoglobin beneath the skin. Its appearance will depend on the depth and size of the injury, the area of the body affected and the person’s natural skin tone.

• Green

As the haem component is broken down, the body produces biliverdin. Biliverdin is a green pigment, which explains why some healing bruises develop a greenish appearance.

• Yellow

Biliverdin is then converted into bilirubin, a yellow pigment.

Yes, the same pigment associated with the yellow colouring seen in jaundice. In a bruise, however, the bilirubin is localised within the injured tissues while the body continues clearing the escaped blood.

Brown and fading

Other breakdown products, including iron-containing pigments such as haemosiderin, can contribute to a brown or golden appearance. Eventually, the pigments are removed and the discolouration fades. The underlying tissues may have repaired before the last visible trace of the bruise disappears.

The pathway from haem to biliverdin and bilirubin is well established, although a real bruise may not display every colour neatly or in the same order. "Research describing the natural history of bruising" explains how the body processes and removes blood from injured tissues.

 

Do all bruises follow the same timeline?

Not exactly. You may see charts claiming that a bruise is purple on a particular day, green on another and yellow by the end of the week. They make the process easy to visualise, but the human body is rarely that organised.

The colour and healing time can be affected by:

• The size, force and depth of the injury
• The location of the bruise
• Age and skin fragility
• Medicines that affect bleeding or clotting
• Circulation and general health
• Natural skin tone

A bruise may also contain several colours at once because different areas can be at different stages of breakdown. This means that colour alone cannot reliably tell us the exact age of a bruise. Research has found that skin tone and bruise size influence how colour changes are measured, so visual appearance must be interpreted cautiously rather than used as a precise clock. "Scafide and colleagues’ bruise-colour study", demonstrated these differences across light, medium and dark skin tones.

What does bruising look like on darker skin?

Bruising is not always well represented in clinical textbooks or educational images.

On darker skin, a bruise may appear deep purple, brown, black or darker than the surrounding skin. Some of the familiar green and yellow changes may be subtle or may not be clearly visible at all.

Other clues may be just as important as colour, including:

• tenderness or pain
• swelling
• warmth
• a change in skin texture
• the patient’s description of what feels different

This matters in clinical practice. If we only look for the classic colourful bruise shown on pale skin, bruising may be underestimated or missed.

Can a bruise move?

It can certainly look as though it has. Blood and tissue fluid may spread through tissue planes or move downwards under the influence of gravity. This means discolouration can appear some distance away from the original injury.

For example, an injury higher up the leg may later produce bruising around the ankle. It does not necessarily mean the person has sustained a second injury there, although the whole area should still be assessed properly.

What can help a minor bruise?

Most uncomplicated bruises gradually improve without specific treatment.

A wrapped cold pack may help reduce pain and swelling shortly after the injury. It should not be placed directly against the skin. Elevating the affected area, where practical, may also help with swelling. "Leeds Teaching Hospitals NHS Trust" provides similar advice for managing minor bruising.

Be careful with pain relief if the person has other conditions or takes medicines that affect bleeding. Students should not recommend, administer or withhold medication outside their level of competence and local policy.

When should bruising be checked?

Bruising is common, but it should not automatically be dismissed, especially when there is no clear explanation.

Medical advice may be needed if bruises:

• appear frequently or without a known injury
• are unusually large, painful or increasing in size
• are accompanied by nosebleeds, bleeding gums or other unusual bleeding
• develop after starting a new medicine
• do not appear to be healing
• occur alongside significant swelling, loss of movement, numbness or weakness

People taking anticoagulants may bruise more easily, but new or concerning bruising still deserves appropriate assessment. Never assume it is “just the blood thinners.”

After a significant injury, bruising combined with severe pain, deformity, reduced movement, worsening swelling or concerns about circulation could indicate something more serious than a simple bruise.

The Bleepbook takeaway

A bruise changes colour because the body is dismantling and clearing blood that has escaped into the tissues.

Haemoglobin and haem are broken down into coloured pigments, including green biliverdin and yellow bilirubin, before the remaining products are gradually removed.

But remember: not every bruise travels through a perfect rainbow, and colour cannot reliably reveal its exact age.

So the next time a bruise changes from purple to green and yellow, you are not watching it become “more bruised.”

You are watching the clean-up crew at work.