Some possible causes may include muscle twitching — breast tissue does have a small amount of muscle in it, and these muscles may involuntarily contract, like a muscle spasm you might feel in a larger muscle. The chest-wall muscles behind the breast tissue might also contract or spasm. Or, if you run or jump with minimal or no bra support, the movement of the breast during such exercise might cause a vibrating feeling that could persist even after you stop the activity. You should mention the feelings that you are having in your breast to your physician. A breast examination that is normal will be reassuring, and, in any event, you should have a screening mammogram every year if you are age 40 or over.
