I have developed a sulfa allergy after many years on antibiotics (so many that we don't put me on them unless absolutely necessary). When you think of a sulfa based allergy, you think of penicillin, biaxin, etc.; but did you ever think of lidocaine? This is a general anesthetic they use before blocks, before root canals or other shots in the mouth, before iontophoresis, before giving you anesthesia for surgery and in patch form as a pain killer. I'm deathly allergic to it, so much so that it will trigger hives all over my body and an asthma attack. I was fortunate in the fact that I found out during iontophoresis so just half my body swelled up like a balloon, and I had trouble breathing (nothing my allergist couldn't handle...he shouldn't have had to, but that's another story).
Anyway, I'm very conscientious about telling people I can't have it, and it's a good thing, cause they were going to inject it before puttin me out for major surgery recently (not a good thing). Fortunately, they did have the one topical anesthetic I can use, mepivocaine.
So if you find yourself itchy after any of these procedures and you aren't sure why, you might want to ask your doctor about how much sulfa you can ingest prior to developing an allergy, and if he thinks that might be the problem. Mine was floored to learn, yes that is the problem (even when he knew I had a sulfa allergy).