Postinflammatory hyperpigmentation
Postinflammatory hyperpigmentation is a cutaneous condition characterized by increased pigment in the skin following inflammation of the skin. Postinflammatory hyperpigmentation can be caused by prolonged sun exposure, inflammation, or other skin injuries, including those related to acne.  People with darker skin tones are usually more prone to hyperpigmentation with excess sun exposure.

      References Postinflammatory Hyperpigmentation 32644576 
      Postinflammatory hyperpigmentation (PIH) is a common acquired cutaneous disorder occurring after skin inflammation or injury. It is chronic and is more common and severe in darker-skinned individuals (Fitzpatrick skin types III–VI). While the condition typically improves spontaneously, this process can take months to years, necessitating prolonged treatment. Combination therapy is the most effective.
       Postinflammatory hyperpigmentation: a review of the epidemiology, clinical features, and treatment options in skin of color 20725554 
      Postinflammatory hyperpigmentation is a common sequelae of inflammatory dermatoses that tends to affect darker skinned patients with greater frequency and severity. Epidemiological studies show that dyschromias, including postinflammatory hyperpigmentation, are among the most common reasons darker racial/ethnic groups seek the care of a dermatologist. The treatment of postinflammatory hyperpigmentation should be started early to help hasten its resolution and begins with management of the initial inflammatory condition. First-line therapy typically consists of topical depigmenting agents in addition to photoprotection including a sunscreen. Topical tyrosinase inhibitors, such as hydroquinone, azelaic acid, kojic acid, arbutin, and certain licorice extracts, can effectively lighten areas of hypermelanosis. Other depigmenting agents include retinoids, mequinol, ascorbic acid, niacinamide, N-acetyl glucosamine, and soy with a number of emerging therapies on the horizon. Topical therapy is typically effective for epidermal postinflammatory hyperpigmentation; however, certain procedures, such as chemical peeling and laser therapy, may help treat recalcitrant hyperpigmentation. It is also important to use caution with all of the above treatments to prevent irritation and worsening of postinflammatory hyperpigmentation.