In one expert review, preventing dark marks meant a daily morning moisturizer plus a broad-spectrum sunscreen with a high SPF (50+), ideally tinted or containing iron oxides so it also covers visible light.
Peer-reviewed review, open access
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What the sources say about dark marks
Dark marks after a breakout are called post-inflammatory hyperpigmentation (PIH). They happen after the skin has been inflamed, for example by acne, an injury or a skin procedure.
Acne-related dark marks often last a year or longer: in one study of people with acne in Southeast Asia, they lasted at least 1 year in more than half of them.
Illustration made for this page. The sample answer shows how Skinby words a result: a visual resemblance, not a diagnosis. Skinby never names serious conditions from a photo.