Periorbital dark circles are dark blemishes around the eyes. There are many causes of this symptom, including heredity and bruising. Causes Anatomical factors Bony structure and prominence of the orbicularis oculi muscle can contribute to infraorbital dark circles. Skin in the lower eyelid is very thin which accentuates subdermal features. Allergies, asthma, and eczema Any condition that causes the eyes to itch can contribute to darker circles due to rubbing or scratching the skin around them. Hay fever sufferers in particular will notice under-eye "smudges" during the height of the allergy season. Atopy can lead to frequent rubbing of the eyes, leading to local inflammation and increased pigmentation. Also, dark circles from allergies are caused by superficial venous congestion in the capillaries under the eyes. Medications Any medications that cause blood vessels to dilate can cause circles under the eyes to darken. The skin under the eyes is very delicate, any increased blood flow shows through the skin. Cortisol deficiency When cortisol is deficient the pituitary compensates by producing excess adrenocorticotropic hormone (ACTH) and melanocyte-stimulating hormone (MSH), the latter resulting in dark circles under the eyes. Anemia The lack of nutrients in the diet, or the lack of a balanced diet, can contribute to the discoloration of the area under the eyes. It is believed that iron deficiency and vitamin B12 deficiency can cause dark circles as well. Iron deficiency is the most common type of anemia and this condition is a sign that not enough oxygen is getting to the body tissues. The skin can also become more pale during pregnancy and menstruation (due to lack of iron), allowing the underlying veins under the eyes to become more visible. Fatigue A lack of sleep and mental fatigue can cause paleness of the skin, allowing the blood underneath the skin to become more visible and appear bluer or darker. Age Dark circles are 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. As facial fat descends and fat volume decreases, the somewhat inflexible ligaments can result in orbital rim and facial hollowing. Photoaging has similar effects. Hemoglobin breakdown products such as hemosiderin and biliverdin can leak from the vascular contributing to pigmentation changes. Circles may also gradually begin to appear darker in one eye than the other as a result of some habitual facial