Dark circles under the eyes (DCLE) are defined as circular, evenly pigmented areas located bilaterally in the infraorbital region. It may be caused by a variety of etiologic factors, including dermal melanin deposition, hyperpigmentation following inflammation secondary to allergy or contact allergic dermatitis, periocular puffiness, superficial capillaries and shadows of loose skin, etc. Little has been written about its pathogenesis. Although dark circles do not cause any pathological changes, threaten health, or cause disease, they can seriously affect one’s mood and self-perception, making one look tired, sad, and lethargic, which makes many people cover up dark circles at work and socially, causing many women to be troubled by them, and even affecting their quality of life. I. Epidemiological study Gupta et al. conducted a controlled study of 32 women with irregular diet and skin problems and 34 healthy women. They found that 9% of the healthy women group under the age of 30 had dark circles under their eyes, while 38% of the group of women with irregular diets had dark circles. The formation of dark circles is related to the following factors: lack of sleep, excessive fatigue, so that the eyelids do not get rest, in a state of tension and contraction, so that the blood flow in the area for a long time to increase, causing the subcutaneous tissue of the eye circle filled with blood vessels, resulting in the eye circle bruising, stagnant under the dull black shadow, so the eye circle is black; long-ill or weak or first recovered from a serious illness, due to the weak subcutaneous tissue around the eyes, the skin is prone to pigmentation The dark circles will appear in women with menstrual disorders, such as functional uterine bleeding, primary dysmenorrhea, early or late menstruation, long periods and excessive menstrual flow. Third, the pathogenesis of dark circles is divided into two colors, one is cyan black circles, which is due to microvascular venous blood stagnation; the other is teal black circles, due to melanin production and metabolism is not complete, two kinds of dark circles produced by completely different reasons. Greenish-black circles usually occur around the age of 20, and are especially difficult to avoid in people with abnormal lifestyle, because of the slow flow of blood in the microvasculature, increased blood volume and oxygen consumption, and the result of a large increase in oxygen-deficient hemoglobin, which makes the skin appear dark blue in appearance. Since there are more microvessels around the eyes, factors such as lack of sleep, eye fatigue, stress, and anemia can cause bruising and puffiness in the skin around the eyes. The cause of tea-black circles is closely related to ageing. Long-term sun exposure causes pigmentation around the eyes, which over time will form lingering dark circles; in addition, blood stagnation causes sluggish melanin metabolism and excessive dryness of the skin, which can also lead to the formation of tea-black circles. In conclusion, dark circles are composed of multiple pathogenic factors, including deposition of dermal melanin, hyperpigmentation after inflammation, mainly hereditary allergies or allergic contact dermatitis, periorbital edema, surface location of the vascular system, and shadows caused by skin laxity. 1. Cutaneous melanin deposition Watanabe et al. performed periorbital biopsies on 12 Japanese patients and showed that all of these individuals had histological melanin deposition. We have conducted epidemiological investigations at the University of Franscomte, France, and the China Medical University, Shenyang, and found that the melanin index was significantly higher at the dark circles of the skin compared to normal skin. This result was confirmed by skin CT (in vivo laser confocal microscopy). 2. Post-inflammatory hyperpigmentation Dark circles are prevalent in allergic patients and patients with atopic dermatitis. In these cases dark circles are due to facial allergies causing periorbital fluid accumulation and frequent rubbing of the periorbital skin. 3. Periorbital edema The eyelid area seems to have a “spongy” character. The edema increases in the morning or after a salty diet, resulting in purple, dark circles. The edema can lead to the formation of shadows underneath, exacerbating the appearance of dark circles. The skin of the lower eyelid is approximately 0.4C0.5 mm thick, which is significantly thinner than the skin of other areas. The results showed that the skin of the dark circles was significantly thinner. When the lower eyelid was stagnant or congested, the dark circles were more visible on the thinner skin. As patients age, atrophy of the subcutaneous periorbital fat and skin may lead to exposure of blood vessels in the eye sockets. The exposed capillary network leads to a blue-gray color around the orbit. 5. Effects of eye bags The dermis of the eyelids contains less collagen, elastin and glucosaminoglycan than other areas, and as patients age they tend to develop eye bags causing shadows. 6, tear trough low pressure The tear trough low pressure is a kind of low pressure concentrated in the middle point of the lower edge of the eye orbit. It deepens as the patient ages, causing loss of suborbital fat, loss of subcutaneous fat, thinning of the skin over the orbital rim ligament and sagging of the cheeks, resulting in a concave shape left in the peripheral appearance part of the eye socket, forming a shadow under light conditions, thus leading to aging of the eyelids and face. 7. Blood circulation around the eyes Masuda et al. applied spectrophotometric measurements to show that the blood oxygen saturation of the lower eyelid skin of people with dark circles was significantly lower than that of those without dark circles. When the skin temperature decreases, the skin vasoconstriction decreases the blood flow to the skin and the oxygen saturation of the lower eyelid skin decreases significantly, thus causing dark circles to appear. On the other hand, Matsumoto et al. reported that the number of skin microvessels in the lower eyelid is greater than that in the cheek, and blood flow is faster than that in the cheek, so stagnant blood flow and blood pooling can contribute to the appearance of dark circles. In addition, the accumulation of iron-containing hemoglobin, a metabolite of insoluble hemoglobin, has also been considered as a factor affecting dark circles.