eli5:Why do bruises under fingernails grow out, but bruises elsewhere just fade and go away?
In: Biology
The ones you see grow with the fingernail are not bruises – bruises are blood under the skin. What you’re seeing under the fingernail is blood ABOVE the skin, trapped between it and the fingernail. The bleeding stops, the blood dries to the inside of the fingernail but can’t get washed off. So, it moves with the fingernail as it grows until it gets cut off or hits open air where washing your hands gets water under that portion of the fingernail.
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