Gynaecomastia typically present as two sided or bilateral growth but in small percentage (less than 5-10%) it can present as one side or asymmetrical.
Unilateral gynaecomastia is very noticeable and brings unwanted attention towards it. This in turns add to psychological burden to it.
Contrary to what you would think , the best treatment for unilateral gynaecomastia is treatment on BOTH side so that result is smoother and symmetrical. There is usually some fullness on the smaller side that benefit from treatment , if not,the smaller side will appear like it has gynaecomastia after treatment.