Hi, as you have mentioned very few symptoms related to the disease as associated itching, pain, fever, extra , so, it is very difficult to say about the causes exactly. But, it can be due to any bacterial infection like staphyloccal/ streptococcal, yeast like fungal infection by candida, and viral infection by Herpes virus all of which are more common in diabetes, so, go for Blood glucose estimation. other causes include- allergic reaction, Angiomas are benign condition containing small blood vessels or lymphatic vessels, acanthosis nigricans which signifies some internal malignancy. So, consult a dermatologist for further diagnosis and treatment. Clean the area properly with mild soap with moisturizer. Thank you for consulting HCM.