There are several different types of birthmarks, such as hemangiomas and pigmented nevi and Mongolian spots, with different types and different causes of formation. The formation of birthmarks is influenced by several factors, such as genetic information or during pregnancy, inappropriate diet or medication of the pregnant woman and external environmental influences. The specific formation of birthmarks, in turn, varies depending on their type. Generally speaking, Mongolian pigment is deposited in the dermis when the fetus is growing and developing in the mother’s body, and it accumulates to a certain amount and then becomes a greenish-gray birthmark, which usually fades to disappear on its own. Bright red birthmarks are mostly hemangiomas, which are formed by the expansion of certain capillaries under the skin and are genetically or genetically related. Some hemangiomas are not harmful to health, but some of them may expand abnormally, squeezing normal tissues or causing rupture and bleeding, etc., and need to be treated promptly. The cause of congenital pigmented nevus is unknown, but its formation is associated with a large amount of melanin accumulation in the basal layer of the skin. If the coverage of pigmented nevus is too large, it should be treated promptly. The causes of birthmarks are related to heredity and some improper dietary habits and medication during pregnancy, and there are many different types of birthmarks.