I have searched the web inceasantly, traveled to the ends of cyberspace trying to find a single consistant answer to this, and seem to get all different answers from everyone.
This has happened to me a few times before, too, so i'm not freaked out by a first time occurance.
After shooting, usually in my wrist or hand, my arm has swelled up and a terrible hell-fire races through my hand and forearm. The intense burning only lasts a few minutes, but it stays swollen for an hour or so.
I use a cotton filter, always make sure I get blood in the syringe before pushing the plunger, and know it can't be an allergic reaction, because the last time this happened, I had already done two or three shots of the same batch, just hours before, and didn't have any problem with swelling or burning.
This also has happened with china white, dirty powder dope, and black tar from as far north as Canada and as far south as Mexico.(most recently with the Tar, and for the first time with tar after using tar for about a month.)
Any insight as to what this really might be?