Post inflammatory hyperpigmentation is the term used to describe a localised area of greater pigmentation, which occurs after some trauma like injury, wound or burns. The pigmentation can be present in the superficial (epidermis) layer or the deeper (dermis) layer.
Following an injury, the epidermal cells trigger an inflammatory response by greater oxidation of arachidonic acid to form prostaglandins and leukotrienes, which are known as the chemical mediators. These substances are the precursors of melanin formation. Also, the fibroblasts start producing more keratinocytes and some enzymes, which promote melanin formation. All these processes lead to an increase in the production and deposition of melanin in keratinocytes. All these changes lead to increased pigmentation of skin at the site.
Sometimes, the injury disrupts the basal cell layer, causing the pigments to escape in the dermis layer. These pigments are then engulfed by circulating immune cells, the macrophages. The pigments are thus embedded deeper inside the skin layer. This condition is known as dermal melanosis. The pigmentation in this case gives a characteristic grey-brown-black hue.
The pigmentation of the epidermal (upper) layer resolves by itself in 6-12 months. But the pigmentation of deeper layer is more severe, and does not generally resolve by itself.
Such pigmentations can result from one or more of the reasons like inflammatory skin disorders (e.g. Eczema, acne), trauma, allergic reactions of the skin, exposure to UV light, etc. The pigmentation can get worsen due to the use certain drugs like antimalarial drugs, tetracyclines, some hormones (e.g. Estrogens), and some anti cancer drugs.
Various management modalities used for the reduction of such pigmentation are:
- Avoid direct sun exposure. Sun exposure may increase the pigmentation and worsen the condition. Use a sunscreen with high SPF before going out in the sun.
- Topical application of various drugs like retinoids (tretinoin), corticosteroids, vitamin C, kojic acid, azelaic acid, hydroquinone and other skin lightening agents may be used. Retinoids are helpful in the reduction of the scar as well. Corticosteroids are generally used in cases of an underlying infection.
- Systemically, vitamin C can be administered, as vitamin C helps in collagen repair and formation. The process of collagen formation and repair results in reduction and repair of the scar.
Prognosis of the upper layer (epidermal) post inflammatory hyperpigmentation is good, as it resolves within 6 to 12 months. The pigmentations of dermal melanosis can stay unresolved for several years as it involves deeper layers. Patients should be made aware of the time taken for the correction of pigmentation.