What are the possible reasons to why my breasts hurt on the sides to the touch?

Breast pain. Mastodynia or breast pain can have variety of causes. Most commonly, hormone fluctuations can cause pain. Fibrocystic disease can also be painful and related to hormonal levels. Less common reasons include infections or inflammatory conditions. In older patients (ie. In the fourth decade of life or greater) an advanced cancer can be painful. See your physician for a good history and physical.