There is a normal physiological line on the abdomen, but when you are not pregnant, most people have a light color of this line and it is difficult to distinguish it, 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. The imbalance between estrogen and androgen secretion during pregnancy causes the pigmentation to deepen and worsen, resulting in the formation of pigmentation on the bottom layer of the skin. Most pregnant women will have stretch marks, which will naturally fade or even disappear within a year after delivery. Some pregnant women will have stretch marks earlier and some 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.