First, there are the complications after any surgery: bleeding, infection, unsatisfactory scars, skin sensation or color change, dimples, ridges, irregularities, subcutaneous firmness, asymmetry, need for re-operation, or more serious complications including, but not limited to, heart attack, stroke, blod clot, or even death. After telling patients this "heavy" list, I usually pause, take a breath, and add "You could also be hit by a bus before having your surgery and then you won't look good at the funeral home." A little lightening to a serious topic.
Specifically to breast reduction, I add the potential for skin loss or nipple/areola loss requiring prolonged bandages, skin graft, or additional revisional surgery, but this occurs mostly (but not always) in smokers. Do NOT have breast reduction, breast lift, facelift, or abdominoplasty (to name a few) if you continue to smoke, use tobacco in any form, or even use nicotine patches, spray, gum, or have exposure to second-hand smoke. This can cause irreversible loss of circulation in the healing skin, and the most sensitive areas can die, requiring the above list of re-dos. Also, there is about 15% chance of losing nipple/areola sensation, which is not a failing of the surgeon or technique, but related to the patient's anatomy. This must be understood and accepted prior to agreeing to this surgery.
All this being said, breast reduction surgery is excellent in the hands of a well-trained, board-certified plastic surgeon with experience in this procedure. Many of my happiest patients are breast reduction patients!