The vagina is not smooth; it is made up of mucous membranes, muscles, and elastic fibers. In women of childbearing age, there are many folds in the vagina, and the folds are arranged in a longitudinal pattern, so the walls of the vagina are very elastic. In the case of young girls or post-menopausal women, the hormone levels are low, which leads to a reduction in the number of folds, a weakening of the stretching of the vagina, and poor local resistance of the vagina, which makes it susceptible to infections. Therefore, for young girls and postmenopausal women, the vagina is relatively smooth, but such smoothness is not good for women.