Blister on scar 6 months post-op, should I be concerned? (Photo)

First of all, don't worry, this area will almost certainly heal up fine. I doubt this small area of incisional breakdown is due to pressure or rubbing from your bra or undergarments. That usually occurs on the lower transverse incision due to wearing an underwire bra too soon after surgery. Since you're now over 6 months out from your surgery and based on the location and appearance of the area, it's most likely either a suture granuloma or an isolated area where a deep suture used to close the incision is "spitting" out though the skin - both are relatively common. In either case, the problem arises as a result of the inflammatory reaction that your body undergoes as the suture is dissolving and being broken down. The history of a small raised area that eventually opened up is consistent with each. The fact that the area is not tender with no surrounding redness or sign of infection is good and further confirms what's most likely going on. The best thing to do is to just treat the area conservatively with bacitracin/triple antibiotic (Neosporin) ointment and cover with a bandaid to protect is from rubbing and shearing. You should be fine wearing a bra as well. If the problem suture has dissolved or already been extruded, the area should heal on its own in a week or two. If it's more stubborn and doesn't close up, depending on which type of suture was used (braided vs monofilament) there may be a prominent portion vs a retained part of the suture knot still in/beneath the skin. Either way, if the area hasn't healed in the next week or two, I'd recommend returning to your plastic surgeon that performed the procedure to have them take a look. Best of luck!

Scars, especially those from breast reductions, can be more prone to friction injury as they can sometimes be less sensate and also the new skin is a lot thinner. As long as there is no sign of anything like infection happening at a deeper level, take care of the wound with antibiotic ointment and gauze. If there does seem to be something deeper like a suture, this can cause breakdown of the overlying skin, although it would be rare for such a large area to open up because of a small suture. Check the bra or garment you were wearing when this happened to make sure there is not a pressure point. If this area does not heal in the next 1-2 weeks, I would schedule an appointment to see your plastic surgeon. 

Thank you for your question.   There are several causes for small wounds to appear along scar lines.  The most common reason for an opening to occur is from a suture spitting from the incision.  Your breast reduction surgery was sutured closed in several layers.  Occasionally, the deep layer of suture may not dissolve, but rather irritate the surrounding tissue and then "spit" from the incision line.  This won't cause any harm to your procedure or your breast.  The small opening will likely heal without issues with conservative treatment (bacitracin or neosporin ointment with a band aid for a week or two).  The best thing to do would be to call your surgeon and have him or her look at it to make sure there are no other issues (infection, etc).  Good luck!