Dark circles under the eyes can be caused by lack of sleep, but that isn't the only reason. Eye tissue is very delicate and certain lifestyle factors can affect sensitive eyes, such as stress, alcohol and smoking. Aging also affects your eyes as your skin becomes thinner, the amount of fat and collagen decreases, and the veins under your eyes become more visible. Dark circles under the eyes can also be caused by skin conditions, such as pigmentation problems or sun exposure. Heredity can also play a part as a factor for dark circles under your eyes. There are also some medical conditions that can cause dark shadows to develop. However, very often under-eye darkness is sign of an allergic reaction, as the eyes and nose are affected by indoor or outdoor allergens that the body overreacts to. Histamine released to fight the offending allergen can cause your eyes to water, itch, swell and redden. If you rub your itchy eyes too much, it can trigger more swelling and redness that may result in dark circles.

Treatment for dark circles starts at home. You can reduce the swelling related to eye allergies with an ice-pack or a cooled tea bag. Sometimes the dark circles stem from nasal congestion, which is also a sign of allergy. The veins under your eyes that drain fluids from your eyes to your nose can swell and become darker when the nasal passages are blocked. Rinse sinuses with a nasal spray, or make your own saline rinse with warm salt water; two cups water and ¼ teaspoon sea salt. If you want to hide the puffiness and discoloration under your eyes, be careful with cosmetics. Some can cause irritation to the sensitive eye tissue that can worsen the redness and swelling, and they can sometimes do more harm than good.