5th June 2025

Post inflammatory hyperpigmentation

Post inflammatory pigmentation is the transient pigmentation that occurs from various triggers such as injury or inflammatory disorder of the skin. It causes melanosis of the epidermal or dermal layer of the skin. It is typically seen in darker skinned individuals.

Causes:

• Inflammatory skin disorders- eczema, psoriasis, lichen planus, acne, systemic lupus erythematosus, dermatitis, cutaneous T-cell lymphoma 
• Injury to skin like thermal burn 
• Allergic reactions
• Phototoxicity 
• Iatrogenic causes- treatment with a fully ablative laser on dark skinned patients 
• Drugs- chlorpromazine, chloroquine, arsenic, tetracycline, bleomycin, doxorubicin, 5 – fluorouracil, busulfan, antimalarial drugs and hormones (oestrogen)
• Ultraviolet light exposure
• Exposure to chemicals- silver, gold, and arsenic
• Idiopathic- No cause identified

Presentation

Hyperpigmented patches occur at the site of the original exposure or insult, presenting as light brown to black macules or patches with poorly irregularly defined borders with minimal surface change. The patches can darken when exposed to sunlight.

Diagnosis

Usually, a history and examination are enough to diagnose post inflammatory hyperpigmentation. When diagnosis is not clear a skin biopsy may be done with histopathology showing patchy epidermal melanosis and/or dermal melanosis. 

A Wood’s lamp can also be used to distinguish dermal from epidermal hyperpigmentation however post inflammatory hyperpigmentation can be dermal or epidermal. Epidermal lesions are generally easier to treat than dermal pigmentation.

Treatment 

Usually, the pigmentation resolves without any treatment. However, it is slow to resolve even with treatment. To prevent further hyperpigmentation, avoiding sun exposure is advised using a high- factor sun cream. If an underlying cause is identified, then treating this will help. Medications that can be used include retinoids, azelaic acid, topical steroid, and hydroquinone. However, there are safety concerns for hydroquinone including carcinogenesis and ochronosis- which is the development of blue-black discolouration of tissues.