Dr Sachin Dhawan, Senior Consultant Dermatologist, Fortis Hospital, Gurgaon and Co-founder, Skin n Smiles says that dark circles happen because of the general loss of fat in the area around the eyes when a person is ill. The skin around the eyes becomes thinner and the veins under the skin tend to become more visible, so, it gives a blueish-blackish look to it, he says. According to Dr Dhawan, dark circles can be reduced by massaging the undereye area gently and using vitamin K or C based creams or serums.