The darkening of the neck skin of pregnant women during pregnancy is caused by the increase in hormone levels during pregnancy, which is a normal physiological change that usually recovers gradually after the end of delivery. The increase in melanocyte-producing hormones during pregnancy strengthens the function of melanocytes in the skin, melanin deposition, and skin color will deepen. Such skin pigmentation can occur especially on the nipples, areola, right in the middle of the abdomen, neck, and vulva. For stretch marks that appear during pregnancy, because of the gradual increase in the size of the pregnant uterus and the increase in adrenocorticotropic hormones during pregnancy, the pregnant woman’s stomach, buttocks, and thighs are altered by the intracutaneous tissue, and the skin is overly expanded and the elastic fibers of the skin are broken and formed. They are usually purple and light red cracks, and can also gradually become lighter and disappear after the end of delivery.