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Are the dark marks aka "moles" on our skin a patch of dead cells? If so, why is it not cleared over time? In a (probably) similar vein, why do scar marks from injuries remain long after new cells replace the dead cells?

[Feel free to edit out the second question if the answers are unrelated]

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up vote 8 down vote accepted

A mole is simply a benign tumour, i.e. a proliferated cell growth that hasn’t become cancerous. So moles are not dead cells, they are very much alive. The colour is caused by a high concentration of the melanin, which is also responsible for normal darker skin.

Since moles are tumours, they can – but in most cases don’t – give rise to melanomas, malignant skin tumours, when they lose susceptibility to cell growth regulation and start invading surrounding tissue.

Scar tissue is entirely unrelated and due to regular regrowth of epithelial cells after injury forming a linear collagen structure (as opposed to the skin’s normal collagen structure, which resembles a “weaved“ structure).

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A Mole may be a Hamartoma or a benign tumor. A congenital mole is usually a hamartoma, while acquired mole a benign tumor. In a few people mole very slowly grow in size.

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