Why does hitting someone (or getting hit) hard causes a bruise? Why is it blue?
In: Biology
The bruise is blood that has leaked, and is being broken down by the body. The colour of the bruise is dependant on how far the blood has been broken down, so it changes from pink-red to blue-purple to green to yellow-brown over time.
Blood with a lot of oxygen is red, blood with less oxygen is more bluish.
These colourings from broken down blood also affect the colour of feces and urine.
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