Breast reduction surgery
can have a few complications. Nipple inversion, also known as invaginated nipple, is a common condition for many conditions. Regardless, I would recommend following up with your surgeon
in order to further evaluate this.
There are a few causes of inverted nipple. After surgery this can occur due to natural restructuring of the breast tissue. Generally speaking, there are many small ligaments in the breast that attach to the nipple and areola. If tension is put on these ligaments in a new pattern, the nipple can be pulled in and therefore cause and inverted nipple. Surgeons work to ensure this does not occur. However, it is possible that it has occurred. One complication that might have caused this is hardening of some part of the breast tissue which changed the structure of the ligaments. Fat necrosis can cause this -- which is hardening of a part of the breast tissue. Other breast masses could cause this.
Other causes of inverted nipple should be considered. A common one is actually pregnancy. You should ensure that you are not at risk for this. Other causes like hormonal problems or infection could also be causing this.
Talk to your surgeon. This should be evaluated. Good luck!