Some unevenness of the breasts or breast asymmetry is normal. There are always some differences in our bodies from side to side. Causes of breast asymmetry can be divided into two broad groups. Asymmetry resulting from natural development, which includes normal pubescent growth, changes resulting from pregnancy, lactation and weight fluctuations. The other general group is asymmetry caused by abnormal external factors such as disease, trauma or surgery. In this article we’ll review some specific breast differences caused by development or other natural causes.
Beginning during puberty and extending through the adolescent years, the female breasts develop, increasing in size and projection and changing form. For most women the differences that exist at the end of this process are minor. In general, the developed breasts have similar volumes, the inframammary folds (the natural lower boundary of the breast where the breast and the chest meet) are similar in position, nipple position is approximately at the same level, and the nipples are at the center of the breast and above the inframammary fold (IMF).
Volume differences are very common and are often associated with differences in nipple position and diameter as well as differences in elevation of the IMF. When the nipple position is below the ideal location the breast is said to be ptotic. This is especially true when the nipples fall below the IMF.
Pregnancy and large weight changes can also lead to many of these differences. During pregnancy and lactation there is a substantial (in most cases) increase in the size of the breasts. This increase in size is largely due to the development of the glands that produce milk. Some of the increase in size is also due to an increase in the fat component of the breasts as weight is gained during pregnancy. After breast-feeding has stopped there is a decrease in the volume of the breast. Usually the breast shrinks back to near pre-pregnancy size, although often there is an additional decrease in overall breast volume. In this situation the post-pregnancy breast volume is actually somewhat smaller than the pre-pregnancy volume. In some cases the process of pregnancy, lactation and post-pregnancy contraction can lead to different changes in each breast resulting in asymmetry. This is often compounded by stretching of the breast skin and the supporting ligaments of the breast leading to lowering of the breast as well as lowering of the nipple position. The ptosis that develops along with the volume changes can cause further differences between the breasts.
Similarly, significant weight changes lead to changes in the amount of fatty fullness of the breasts. As weight increases, the fat portion of the breast increases and conversely as the weight falls, the fatty portion decreases. Again, this process can occur unevenly on each side leading to asymmetry which can also be compounded by the same stretching of the skin and supporting ligaments of the breast just as in pregnancy.
Tuberous breasts are a condition of abnormal breast development. In this breast type the base diameter of the breast is constricted leading to a breast which is not conical in shape but rather has more of a tube shape. The areolas are often larger than normal in diameter and often are much lower than the inframammary fold. This type of breast development may occur on only one side leading to significant volume and shape differences.
Treatment of each of these causes of asymmetry and their combinations are varied according to what conditions present. Details and choices of treatment possibilities will be discussed in subsequent articles.