The cause of spider nevus is not necessarily cirrhosis of the liver. The main reason for spider nevus is the dilation of small arteries under the skin, which is mainly caused by the inactivation of estrogen. Estrogen is mainly inactivated in the liver, and when liver function decreases, the inactivation of estrogen decreases, causing a higher concentration of estrogen in the blood, which causes the small arteries to dilate and manifest as spider nevus changes. When liver function declines mildly, it does not affect estrogen inactivation. In cirrhosis, liver function declines significantly, so the formation of spider nevi is often seen in patients with cirrhosis. In addition to impaired estrogen inactivation, high estrogen levels can also cause spider nevi, mainly in pregnant women. Due to the change of hormone level after pregnancy, especially the estrogen level is obviously increased, the formation of spider nevus can also be seen in pregnant women, so we cannot judge that a patient has cirrhosis based on the appearance of spider nevus alone.