There is a normal physiological line on the human abdomen. However, when you are not pregnant, most people have a light-colored line that is hard to distinguish, and some people who are not pregnant also have a faint black line. Usually, this line on the stomach will be aggravated when you are 2-4 months pregnant, thus drawing attention to it. This line is also known as the pregnancy line and is a normal reaction to pregnancy. It is formed due to the imbalance between estrogen and androgen secretion during pregnancy, which deepens and worsens the pigmentation, resulting in the deposition of pigment on the bottom layer of the skin. Most pregnant moms will have stretch marks, which will usually fade or even disappear naturally within a year after delivery. Some pregnant women will have stretch marks earlier and some will have them later, but there is no special pattern or effect. Pregnant women with lighter colored skin will have stretch marks earlier and they will be more visible. Therefore, the appearance of stretch marks and their visibility are also related to the underlying skin color. It is recommended that pregnant women should pay attention to eat more vegetables and fruits after pregnancy, reasonably supplement vitamins, and pay attention not to eat spicy and stimulating food to avoid frequent stimulation of the skin, aggravating skin pigmentation.