Image of uneven pigmentation
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To protect itself from the damaging effects of the sun, your skin increases its production of the dark brown pigment called melanin. The extra melanin makes your skin look darker or sun-tanned. In some cases, the sun causes an uneven increase in melanin production, which produces irregular coloring or pigmentation of the skin. The sun can also cause a permanent stretching (dilation) of small blood vessels, giving your skin a mottled, reddish appearance.