What Exactly is a Bruise and Why Does it change so Many Colours?

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This week's post is brought to you by the fab little wisdom of The New Scientist's: 'Does Anything Eat wasps and 101 Other Questions'...How the Heck to Bruises work?

We've all had a good few bruises in our lives. I don't know about you, but as I kid I could pinpoint the exact origin and history as each bruise, but as I get older I find that they seem to spontaneously sprout on my body without any memory of them at all - our bodies cheerily working away to heal us when our big busy brains are occupied on other things. (Well, there are certain exceptions, such as thigh-high furniture corners that are impossible to not notice when you bounce off them like a howling pinball. I'm looking at you, bed!)

However you get them, bruises are certainly strange, often transitioning from reds to purples to greenish-yellows. As with most things colour-related, this is down to their changing composition.

Bruises occur when small capillaries (that is, blood vessels) break under the skin in response to pressure. Haemoglobin  in the blood gives the bruise it's reddish purplish colour. noticing that something is wrong, our usual little saviours the white blood cells rush in to help the healing process. to do this, they start to break down the Haemoglobin, which creates various breakdown products that start to change the colour of the bruise. the red lessens as the haemoglobin deteriorates and biliverdin and bilirubin - green and yellow respectively - are created. these sit around until these are in turn cleared and finally the bruise fades.

The curious thing about bruises is that they offer a snapshot into what goes on in our body every day, even before we launch ourselves at furniture. this breakdown of haemoglobin happens all the time in our blood when the red blood cells have grown old and expired. Our white cells will break down these cells, and then the remaining waste bilirubin is taken up to the liver where it is converted for bile - the same substance that digests your food and causes that awful acid taste when you vomit. if you have too much waste bilirubin hanging about in your body, it turns the skin yellowish as jaundice.

You might find, especially as an adult, that you've forgotten how you got a bruise, namely because they can appear a long time after the injury itself. This is down to blood again: often the injury might be sustained deep in the tissues of the afflicted body part. Since bruises are effectively leaked blood, sometimes it can take a while for them to reach the surface, and might even appear some distance away from the original injury.

Our bodies , as ever, continue to be equal parts awesome and a little gross. Just maybe hold off on the research for this one, ok?

'Contusion Confusion' - Does Anything Eat Wasps and 101 Other Questions - New Scientist (via reader submissions from Claire Adams, Frankie Wong and Stewart Lloyd)
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