The vertical black line on the abdomen of a woman is the stretch mark. How long it takes to recover varies from individual to individual and cannot be generalized. After pregnancy, the level of estrogen, progesterone and chorionic gonadotropin in the body will increase and endocrine changes will occur. After childbirth, the hormone level in the body decreases significantly, so the stretch marks, melasma and hyperpigmentation will gradually fade or disappear. However, due to different body types, the time for stretch marks to disappear is not exactly the same, ranging from 6-10 months to 3-4 years after delivery, and some women may even have them for life. Stretch marks themselves have no effect on health, so there is no need to worry too much. If you feel that they affect your beauty, you can go to a dermatologist and seek professional help.