Hi Paddybrads. I’m not sure of the right answer. Some of the other scientists in the Calcium Zone are much better than me at questions about human bodies. You could ask them if you like. It’s a good question.
A bruise happens when a part of the body is hit and the muscle fibres and connective tissue underneath are crushed but the skin doesn’t break. When this happens, blood from the ruptured capillaries (small blood vessels) near the skin’s surface escapes by leaking out under the skin. With no place for it to go, the blood gets trapped, forming a red or purplish mark that’s tender when you touch it — a bruise.
Bruises change colour over time and that’s your body fixing the bruise by breaking down and reabsorbing the blood, which causes the bruise to go through many colours of the rainbow before it eventually disappears. You can pretty much guess the age of a bruise just by looking at its colour:
When you first get a bruise, it’s kind of reddish as the blood appears under the skin.
Within 1 or 2 days, the haemoglobin (an iron-containing substance that carries oxygen) in the blood changes and your bruise turns bluish-purple or even blackish.
After 5 to 10 days, the bruise turns greenish or yellowish.
Then, after 10 or 14 days, it turns yellowish-brown or light brown.
Finally, after about 2 weeks, your bruise fades away