hello, welcome to hcm. there are lot of reasons for dark circles with rashes most common ones are- heredietary, Allergies, asthma, and eczema,fatigue, age, anaemia, some liver problems etc. this is due to excess melanin pigments produced. most common treatment prescribed are hydroquinone solution often mixed in an oil free moisturizer that acts like a skin bleach. you can continue treatment of your dermatologists. along with it take plenty of water, green vegetables, rub cucumber juice and potato over dark areas, they also help to reduce pigments take care and you can ask future queries