What is the cause of postinflammatory hyperpigmentation?
Inflammatory responses of the epidermal skin layer to disease or trauma results in the release and oxidation of arachidonic acid to prostaglandins, leukotrienes and other products. These products alter the activity of immune cells and melanocytes. Melanocytes produce more melanin (skin colour pigment), which is transferred to surrounding keratinocytes (skin cells). This is known as epidermal hypermelanosis. Another cause is dermal hypermelanosis, a deeper pigmentation that occurs when inflammation disrupts the basal cell layer (the bottom of the epidermis), causing melanin pigment to be released into the papillary dermis (the top part of the dermis). The pigment may be trapped by large immune cells called tissue macrophages.
