 Fat tissue surrounds the mammary glands, and its volume will normally vary throughout life.Although the exact mechanisms that determine breast shape and size are largely unknown, the amount and distribution of fat tissue and, to a lesser extent, mammary tissue, cause variations in breast size, shape and volume.Some experts believe Cooper's ligaments, which are connective tissue with the breast, provide some support within breasts, but there's no agreement on whether they provide support or simply divide breast tissue into compartments.