There are so many other reasons to form the dark circles under the eyes,the common factors are
1)Stress-such as excessive workload,money problems,family problems can cause dark circles under the eyes.
2)Aging-When your age increases your skin become dry an thin and the dark circles become very clear.
3)Lack of sleep-should sleep at least 8 hours of sleep each day.
4)Dehydration-lack of water through the body may cause skin weak and dry.
5)Deficiency of nutrients-Nutrients such as vitamins,minerals,proteins are required for the body's development.Following a proper diet can prevent the dark circle formation under the eyes.
6)Deficiency of Iron(Anemia)
7)Allergies and Allergic(pollen) fever
8)People doing night shift jobs.