PHBruises change color because they're losing oxygen
A bruise is caused by bleeding under the skin; tiny capillaries (blood vessels) are crushed, which expel blood that's trapped under the skin. Initially, the bruise will just look red because the blood is still oxygen-rich. You do not have permission to view the full content of this post. Log in or register now., the blood begins to lose its oxygen, turning purple. Then, after three or more days, bruises will start to turn green, yellow, or grey thanks to compounds called biliverdin and bilirubin that break down the hemoglobin to absorb vitamins and minerals (like iron) for the body to use. The rest of the waste is eventually purged from or absorbed by the body.
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