Cold sore with lip injections? What do I do?

Treat the cold sore as you would if you did not have lip fillers. 3 to 4 months suggests the filler will be harmoniously infiltrated through out your lip tissues so no harm should occur.

Although reactivation of certain viruses are quite possible after physical trauma associated with filler injections, these occur usually very soon after the injection. If your filler was injected 3-4 months ago, the expression of virus in your case is most likely a coincidental issue. If it happens you start oral treatment as soon as possible; if you are at the blister stage, the course will be only partially affected by the medications. The topical antiviral at this stage are of no use for many reasons. I would also consider taking oral medication for 2-3 doses as a profilaxis after your next injections. These antiviral medications are very safe and can be taken in very large doses over extended period of time without any side effects, e.g.. in immunocompromised patients after organ transplant. Good luck!