This looks like an allergic or hypersensitivity response to the skin adhesive your surgeon used. Though the vast majority of patients do not have this response to surgical adhesives, you appear to be in a tiny minority who do. And although this is (almost certainly) self-limited and not of concern, it is natural to consider alternative diagnoses of greater concern, just in case we might be wrong.
Since your skin glue "just came off" on post-op day 12, it is likely that your incision is sealed and intact (and it looks that way in your photograph, but in-person evaluation is better). But is it possible that in the glue "coming off" a tiny opening may have been created in the not-yet-completely healed and durable incision line? Could bacteria enter this microscopic opening and an infection be starting? Doubtful, but possible, and direct examination (and possibly a few days of oral antibiotics) may be in order. If in fact it turns out to be an early infection (I don't really think it is, but then again, I haven't seen anything but your photograph), hydrocortisone cream will NOT be a good thing.
If you and most of us here are right in diagnosing an allergic reaction, simply washing the skin gently and keeping it dry and protected while observing for further redness and irritation is really all that is needed. Hydrocortisone cream may help minor inflammation improve, but this already looks minor, and it should already be better after two days.
BTW, the most common patient response to incisional appearance such as this would be application of antibiotic ointment. This, of course, is because patients more commonly worry about infection rather than hypersensitivity or allergic reactions! Applying Bacitracin (single antibiotic ointment) would likely be unnecessary but non-harmful, and the (probable) allergic response would settle on its own.
But many patients would choose Mycitracin or Neosporin (triple antibiotic) ointments, and Neomycin (the third antibiotic in these onitments) causes allergic reaction with repeated application in as many as 10% of the population, so redness, inflammation, and even open blisters could form, looking just like an infection (most people think of infection first, not what's really going on--a hypersensitivity or allergic response). The usual response is to glop on more triple antibiotic ointment, making things worse! I've even seen patients with this who saw their regular physician before returning to their plastic surgeon, and their doctor prescribed strong oral antibiotics for what looked like a worsening infection, when in fact the only thing necessary was to STOP the ointment! Wrong diagnosis leads to incorrect treatment, and leads to problems getting worse (and more expensive), not better!
So the best advice of all: see your plastic surgeon, who has the most vested interest in making the proper diagnosis and responding appropriately. Self-diagnosis and treatment is not recommended, especially if you end up being wrong! Best wishes and Happy New Year!