What is P.I.E. — and how is it different from PIH (post-inflammatory hyperpigmentation)?

Both are post-acne marks; the mechanism is different, and the treatment differs accordingly.

• P.I.E. — post-inflammatory erythema. The flat pink, red, or purplish marks left behind on the skin where a breakout used to be. The mechanism is vascular: the small blood vessels in the surrounding skin became dilated and persistent during the inflammatory phase of the acne lesion. P.I.E. is most visible on lighter skin tones (Fitzpatrick I–III) and tends to fade slowly on its own over months but is treatable with the right formula.
• PIH — post-inflammatory hyperpigmentation. The flat brown, tan, or dark patches left behind after a breakout. The mechanism is pigmentary: melanocytes were stimulated during the inflammation and deposited extra melanin. PIH is most visible on Fitzpatrick III–VI skin tones and overlaps in treatment with melasma and other hyperpigmentation patterns.

Why this distinction matters: brightening agents like hydroquinone, azelaic acid, and tranexamic acid are designed to address pigmentary marks (PIH and melasma). They do not effectively address vascular marks (P.I.E.). P.I.E. responds better to anti-inflammatory and barrier-supportive actives, careful sun protection, and time. Using a melasma formula on P.I.E. won't help.

If you are unsure whether your post-acne marks are P.I.E., PIH, or a mix, A board-certified dermatologist team will identify the pattern from your photos and prescribe accordingly. Many patients have both.