Spider nevus is a common skin disease in dermatology clinics. It looks like a red spider lying on the skin, so people have given it a very imaginative name – spider nevus, also known as spider capillary dilation or arterial spider nevus, vascular spider or stellate nevus. Don’t underestimate spider nevus, a small spider nevus is a skin sign that most often occurs in cirrhosis of the liver. Why do spider nevi develop? The formation of spider nevus may be due to arterial capillary dilation caused by an increase in the concentration of estrogen in the blood. Estrogen is a sex hormone produced mainly by the ovaries of women. The adrenal glands also produce some estrogen, so spider nevi can occur in both men and women. Estrogen metabolism takes place in the liver, and when liver function is impaired, it accumulates in the body and capillary dilation occurs, which becomes spider nevus, so spider nevus is of great reference significance for diagnosing liver sclerosis. What does a spider nevus look like? The lesion of spider nevus is a red dotted papule with a central protrusion, varying in size from a small one like a large pin cap to a large one with a diameter of more than 1 cm, and the capillaries around the nevus are dilated and have small red blood vessels distributed radially around it, like a spider. What kind of people does it occur in? Spider nevus is common in acute and chronic hepatitis or hepatic steatosis, but also in women during pregnancy (often appearing in the second to fifth month of pregnancy) and in healthy people, alcoholics, people who work hard, patients with severe malnutrition, a few people with rheumatic fever and scleroderma, or people receiving estrogen therapy. The incidence of spider nevus in patients with acute hepatitis is about 1%, while in chronic hepatitis it can be about 54%. The appearance of spider nevus often parallels the state of liver function. When liver function deteriorates, spider nevus may increase sharply; when liver function improves, the nevus may change from bright red to brownish-black and then disappear. It is not uncommon in normal people, especially in children. 38% of children without liver disease may have at least one spider nevus, commonly between the ages of 1 and 4 years, and in normal people there are usually no more than 3 spider nevi. The spider nevus is mainly concentrated in the area where the superior vena cava is distributed, such as the neck, face, upper forehead, back of the hand and dorsal side of the fingers, upper arm, etc. It is rare in the palm of the hand and hairy areas such as scalp and armpit, but it can occur in the skin with long beard and chest hair, not in the mucous membrane of nose, lips and cheeks, and rarely in the abdomen and lower limbs. There is usually only one spider nevus, but occasionally several of them appear at the same time, especially when there is liver damage. Because spider nevus is often found on the face and neck, and is more common in women and children, it affects the patient’s appearance and easily brings psychological stress to the patient, so how to treat it is of utmost concern to the patient. Traditional treatment methods include sclerotherapy, cryotherapy and electrotherapy, etc. They have certain therapeutic effects, but at the same time there are some more serious adverse reactions. Seeking a good treatment effect has always been the goal of medical practitioners, and in recent years, laser treatment for spider nevus has been more widely used. The 585 pulsed dye laser is suitable for patients whose papules are not obvious in the center of the rash and whose surrounding capillaries are superficial, thin and numerous, while the Nd:YAG laser and CO2 laser are effective in treating patients whose papules are obvious in the center of the lesion. For patients with recurrence despite multiple treatments, local excision is feasible. Do spider nevi fade on their own? Ninety percent of the lesions that occur during pregnancy may fade on their own about 3 months after delivery, or they may persist and appear in the same area during another pregnancy. In children, the lesions tend to persist, but a few may fade on their own. Spider nevus due to liver disease varies according to the progression of liver disease.