Hello,
It can be due to fungal infection or erythrasma skin. In erythrasma, the typical appearance is well-demarcated, brown-red macular patches. The skin has a wrinkled appearance with fine scales.
It has to be differentiated from contact dermatitis, psoriasis, sweat dermatitis and fungal infections which may mimic it. Wood lamp examination and gram staining are the tests for its diagnosis.
So nothing can be confirmed without examination. It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
I think you need to see a doctor for proper diagnosis and treatment. It might be caused by a fungus or bacteria. If you can't see a doctor, you could try putting 10 drops of tea tree oil into a mild liquid soap and cleansing daily. It smells like tourpentine, but it kills fungus and bacteria.