Purple/blue liquid bubble on incision 4 months after surgery. Do I pop it and apply bacitracin or leave it alone? (Photo)

It appears that you may have a suture or a deeper fluid collection trying to surface. I would definitely call your surgeon and make an appointment. It would be best to let he/she take care of it to prevent infection or further delayed healing.

A collection of form material such as though suture can lead to a stitch abscess. This is a problem that should be shown to your surgeon. He may be able to intervene and shorten the healing process. Necessitating fat necrosis is a possibility as well.

Stitch abscesses often present as raised, irritated, "infected" areas of skin along an incision line.  These are always best addressed by your Plastic Surgeon, as they best know your anatomy and the suture types placed during your breast reduction surgery.I would avoid opening any wounds or attempting to retrieve "spitting" sutures as this could lead to a much bigger problem such as an infection of the breast or chest wall.  Your surgeon will be able to deliver the best care, such as obtaining cultures if indicated, prescribe medications such as antibiotics if indicated, instruct in proper wound care if indicated, etc. I always instruct my patients to call me first with any problems, and I am sure your surgeon would want the opportunity to help you through this issue.  Good luck!