I have dark circles around my eyes. what could be the possible reasons and how to reduce them?

Usually...: ...Either sleep deprivation or allergies. If sleeping reasonably well--if have bed partner, ask about snoring / tossing & turning / etc.--then, if no contraindication, can try a non-sedating antihistamine like zyrtec (cetirizine) once daily in evenings and see if any change in a few days. If yes, then should talk to your dr about seeing an allergist. If sleep concern, may need sleep study.