If your question is why is a scar white then it is because usually a scar is formed when there are stitches or a scratch on your skin. So when you have a scratch the upper layer of the skin which is tanned goes away and exposes the inner layer of the skin skin which is not tanned so it will be fairer that the outer skin. This the same case even with the stitches. When yu have stitches the inner layer of the skin is seen.

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if this did not answer your question....make sure that your question is more clear and mention which kind of scars...