Spider nevus may be caused by normal physiological factors, or it may be caused by pathological factors such as liver disease, rheumatoid arthritis, rheumatism, Cushing’s syndrome and so on. 1. Physiological factors: the appearance of spider nevus may be caused by the dilation of skin blood vessels due to the elevated level of estrogen in the body, which is not necessarily a disease state. For example, when children are in developmental stage, estrogen level will increase, and spider nevus may appear. Some young women, especially pregnant women, may also have elevated estrogen levels and may develop spider nevi. 2. Pathological factors: when patients suffer from certain liver diseases, such as acute and chronic hepatitis, cirrhosis, liver cancer, etc., it will affect the function of liver cells, so that the inactivation of estrogen by the liver is impaired, leading to the increase of estrogen level in the body, and then spider nevi may appear. In addition, diseases such as rheumatoid arthritis, rheumatism, and Cushing’s syndrome may also result in the appearance of spider nevi. If a patient develops spider nevi for a long period of time or repeatedly, it is recommended to consult a doctor in time to identify the cause of the disease and carry out targeted treatment to avoid delaying the condition.