Why do bruises go purple?

José Monteiro from the National Science Museum explains all.

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Why do bruises go purple?

Sometimes we trip over or hurt ourselves in other ways. When it happens some of our blood vessels break, blood piles up under our skin and we can see this as a bruise. These nasty things have the familiar ‘black and blue’ or purple appearance in the beginning but gradually change into different colours.

The purple colour is given by haemoglobin, a protein that carries the oxygen in our red blood cells. Our body reacts to this with some white blood cells called phagocytes ‘eating up’ the materials in the bruise. As the phagocytes degrade the haemoglobin, they turn it into other molecules. As you can imagine, different molecules show different colours and the bruise will change colour with time to green, yellow and brown. When everything has been cleared up by your immune system the bruise disappears and you’re ready to bump into something else.

Answered by Science Museum Explainer José Monteiro.

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  • Tor Marquis

    In 2008, the Alaska Department of Fish and Game reported that 146 million salmon were commercially harvested. Of this, 60 million salmon were identified as ocean ranched. Therefore, in 2008, ocean ranched salmon represented over 41% of the commercial catch in Alaska. This is already a big reality.

  • http://www.orcasafe.org Christopher Porter

    Tor showed that it already is happening and needs to continue to happen. Hatcheries for wild release and fish farming for food have completely different focuses. The oceans need to be re-stocked by the same ones that emptied them… US!