PIH (post-inflammatory hyperpigmentation) is the flat brown, purple, or gray mark left after the skin heals from inflammation — acne being the most common cause. It's a pigment problem, not a texture problem: the skin's surface is smooth, but melanocytes (the cells that make pigment) overproduce melanin during healing.
PIH vs. Acne Scars
True acne scars are textural — indentations or raised areas where tissue was damaged. PIH is flat discoloration. The good news: PIH will fade over months on its own; treatments like chemical peels, microneedling, and PiQo4 toning can dramatically accelerate that timeline.