The breast consists of milk ducts and glands, surrounded by fatty tissue that provides its shape and fee. Situated beneath the breast is the pectoralis major muscle, a large muscle that assists in chest movement, and where a breast implant is placed when having submuscular breast augmentation. Factors such as pregnancy, rapid weight loss and the effects of gravity as you age, combine to stretch the skin, which may cause the breast to droop or sag. Some women also have a variation in size or shape from the right to left breast, which is called asymmetry. Having either breast augmentation or a breast lift may help with this.