Brief Answer:
Explained

Detailed Answer:
Hello again.

Firstly it may be normal changes with aging on the skin exposed to light
Pigmentation of skin occurs in which people produce excess of melanin these are harmless
Contact dermartitis makes skin inflammed after contact with certain things that can to result in it
harmonal abnormalities like in polycystic ovarian syndrome due to abnormal levels of .harmones skin can have darkened patches seborrheic keratosis in which people develop brown patches .
Melasma is brown patches which women develop during pregnancy due to harmonal changes
Tinea versicolor or pitytiasis versicolor in which yeast species indect the skin to cause brown patches
Neurifibromatosis type 1 people may have small brown spots on skin.
Statis dermatitis in which blood collects in some areas like legs and ankles and resultin staining of skin
Brown skin patches are common in diabetes due to changes in small blood vessels also called shin spots caused by diabetic dermopathy .
Some blood disorders can results in such type of skin lesions
Actinic keratosis is a condition in which keratinoctes grow abnormally may result in brown patches
In XXXXXXX disease the symptoms develops slowly and may involve darkening of the skin
Cushing syndrome in which there is high levels of cortisol can result in hyper pigmentation of skin
Over use of corticosteroids alcoholism and malnutrition can also cause it
Kidney conditions like chronic kidney failure medullary cystic kidney disease can cause skin changes.
Clinical co relation should be done .

let me know if you have any query or need any clarification

You can discuss thsee probable options
with your doctor /dermatologist.

Hope it helps
Thanks

Dr M.S Khalil.

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