Hyperpigmentation is a discoloration of the skin that causes it to be darker than the original pigmentation. It can affect a small area or may be diffuse. Hyperpigmentation is most commonly worsened by sun exposure. The pathogenesis of hyperpigmentation is not completely understood but is thought to involve prostaglandins and leukotrienes, stimulating epidermal melanocytes. The melanocytes disrupt the basal layer of the skin, leading to the deposition of melanin in the dermis.

Hyperpigmentation is caused by several factors:

  • Inflammation from acne, systemic disease, or infection
  • Trauma to the skin
  • Genetics
  • Pregnancy (Melasma)
  • Metabolic disorders, including insulin resistance and deficiency of vitamin B12 and folic acid
  • Medications

Source: Desai S. R. (2014). Hyperpigmentation therapy: a review. The Journal of clinical and aesthetic dermatology, 7(8), 13–17.