Post-Inflammatory Hyperpigmentation
Post-inflammatory hyperpigmentation (PIH) is dark spots left behind after skin inflammation or injury heals, especially common in darker skin tones, per comprehensive dermatology reviews.
Symptoms
Flat brown, gray, or dark patches at the site of a prior pimple, rash, cut, or procedure; the patches can persist for months to years after the original inflammation has resolved.
Causes and risk
Acne, eczema, psoriasis, and skin injury (including from lasers and chemical peels) all can trigger PIH by prompting excess melanin deposition, per the epidemiology and pathogenesis literature; Fitzpatrick skin types III-VI are disproportionately affected.
How it is evaluated
Diagnosis is visual, based on the history of a prior inflammatory event at the same site; a Wood's lamp can help distinguish epidermal from dermal pigment.
Treatment
Treating the underlying inflammatory condition first is essential, alongside daily tinted sunscreen. Hydroquinone and non-hydroquinone topicals (azelaic acid, niacinamide), plus chemical peels, are supported by the AAD-affiliated Delphi consensus on acne-associated hyperpigmentation; lasers are used cautiously in darker skin tones given the risk of worsening pigment.
When to seek care
PIH itself is cosmetic, not dangerous. Seek evaluation if the underlying condition causing it (an infected wound, spreading rash) is worsening, or if a pigmented spot changes in ways atypical for PIH.