Birthmarks are congenital diseases with complex causes, so there is no effective method to prevent the growth of birthmarks. Birthmarks are abnormal growths of skin tissue during development, mainly caused by the deep dermis where melanocytes stay during the migration from the neural crest to the epidermis during the embryonic period, and are affected by genetic factors, environmental factors, and dietary factors. The birthmark may appear at birth or may surface gradually in the first few months after birth. In the first 3 months of pregnancy, we should pay attention to our eating habits and minimize the consumption of contaminated food and vegetables in order to effectively avoid genetic mutation in human body. Therefore, birthmark cannot be prevented directly, early detection, early diagnosis and early treatment are important to prevent birthmark. During pregnancy, the intake of contaminated food and pigmented food should be reduced, while avoiding radiation, drinking more warm water, eating more fresh fruits and vegetables, and eating a light diet is appropriate.