The human abdomen has a normal physiological line. However, when you are not pregnant, most people have a light color line that is hard to distinguish, and some people have a faint black line even when they are not pregnant. Usually, this line on the belly becomes more prominent between 2 and 4 months after pregnancy, which draws attention to it. This line is also known as a stretch mark and is a normal reaction to pregnancy. It is formed due to the imbalance between estrogen and androgen secretion during pregnancy, which deepens and aggravates the pigmentation and causes pigmentation of the underlying skin. Most pregnant mothers will have stretch marks, which usually fade naturally or even disappear within a year after delivery. Some pregnant women will have stretch marks earlier, while others will have them later, but there is no special pattern or effect. Pregnant women with slightly lighter skin color will have stretch marks earlier and more pronounced. Therefore, the appearance and visibility of the stretch mark is also related to the underlying skin color. It is recommended that pregnant women should pay attention to eating more vegetables and fruits after pregnancy, take reasonable vitamin supplements, and pay attention not to eat spicy and stimulating foods to avoid frequent stimulation of the skin and aggravate skin pigmentation.