Lupus can cause a dirty looking area on your skin from UV called Post-inflammatory Hyperpigmentation-this is mine. I used to get horrible itchy rashes right in the same spot but this summer something different happened. And it’s a melatonin reaction-…..who knew?
Hyperpigmentation occurs as brown macules or patches, often with a poorly defined border, irregular in outline and usually with little surface change.
The basic mechanism in response to various triggers (see ‘Causes’, below) is melanosis of the epidermal or dermal layer of the skin. A number of inflammatory mediators, including prostanoids, cytokines, chemokines as well as reactive oxygen species, are released during the inflammatory process in the epidermal layer. These stimulate melanocytes to increase the production of melanin. In dermal melanosis, inflammation disrupts the basal layer, causing melanin to be released and trapped in the macrophages of the papillary dermis – a process with the delightful name of pigmentary incontinence.
Pigmentary changes are much more common in darker-skinned individuals of Asian or African origin and pigmentation follows many common inflammatory diseases such as eczema, psoriasis or acne. Where erythema is seen in white individuals, pigmentation occurs in dark-skinned individuals.
Pigmentation due to increased melanin is a dirty brown colour, as opposed to that due to haemosiderin pigmentation following purpura, which is more a rusty brown colour.
Hyperpigmentation on the face may be due to pregnancy or taking the contraceptive pill (melasma/chloasma).
Other conditions which may enter into the differential diagnosis include:
Amyloidosis – lichen or macular
Another good site on hyperpigmentation : http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3645767/