My guess with your almost instantaneous itching and swelling, that it's either a bite of some kind or your hands worked up a good sweat and some kind of pollen that you might be allergic to got into your pores.
My step-son last year had something similar happen to his arm, but it was over a couple day's and turned out to be a serious super staff infection, that apparently entered his blood system through the hair follicles on his arm.
Doctors had him in the hospital for 3 day's on high dose antibiotics, and just barely kept it from getting into his bone marrow.
But his whole arm swelled up and turned blood red!
To this day, he doesn't know how he picked it up, there was no scratches, cuts, or breaks in the skin.
Phil
