Postinflammatory hyperpigmentation (PIH) describes localized darker skin areas as a consequence of trauma and/or inflammation. It can arise in all skin types but affects patients with darker skin phototypes with greater frequency and severity. There is no age or sex predilection.

The inflammatory process may be incited by an infection, allergy, drug reaction, mechanical or thermal injury, phototoxic eruption, or an intrinsic skin disease.

Although clinically benign, patches of PIH can cause significant cosmetic and psychosocial distress.

Inflammation may induce overproduction of melanin in the epidermis through the effect of inflammatory mediators such as metabolites of arachidonic acid and reactive oxygen species. PIH in the dermis results from damage to basal keratinocytes with release of melanin subsequently phagocytosed by dermal macrophages. Most lesions are a combination of epidermal and dermal pigmentation, the latter being more difficult to treat.

The lesions of PIH may be accentuated by sunlight.