If your breast reduction is carried out by a qualified plastic surgeon, complications are extremely rare and usually insignificant.
Nevertheless the outcome is never completely predictable, as people differ in their anatomy and the healing process may vary from patient to patient.

Complications such as bleeding or infection after a breast reduction are very rare, but if they do occur, they may lead to more extensive scars. You can significantly reduce the risk of complications by carefully following the advice of your plastic surgeon both before and after the operation.
A breast reduction leaves visible scars, although these can be concealed by a bra or swimwear.
Smokers have an increased risk of poor wound healing and broader scars as smoking inhibits the flow of blood in the skin and can thereby lead to disorders in the healing of the incisions.
In rare cases the nipples may be asymmetrical following a breast reduction or there may be a complete loss of feeling in the nipples and the ability to breastfeed may be restricted or lost completely.