What Causes Uneven Breasts [Uneven Boobs]? Lopsided breasts, or very uneven breasts, are known in the medical world as breast asymmetry. Your breasts can grow to appear this way due to several different possibilities: Uneven adolescence development Virginal hypertrophy following puberty Pregnancy Breastfeeding Breast Infection Aging Shrinkage caused by a medical condition Weight change Mastectomy Previously-botched breast augmentation How Common