Dark discoloration of the skin under the eye is mainly referred to as dark circles. Some of the main causes behind the formation of dark circles are heredity, aging, dry skin, mental or physical stress, lack of sleep and an unhealthy diet. 

Dark circles are not a serious skin problem, but they make people look tired, exhausted, unhealthy and older. They are also likely to become more noticeable and permanent with age. This is because as people get older, their skin loses collagen, becoming thinner and more translucent.