AgX, an interesting reaction. I've not used Ultrafin before, but am assuming it came in a highly concentrated solution. it seems to me that you have an allergy to one (or possibly several) chemicals in the 'mix' which made you break out in blisters. May I say, I'm relieved that no further harm came to you as the result of contact with those few drops. An interesting story, many thanks for having posted it.
Back in the late 1950s, when I was a wee nipper in my early teens and the world was a vastly different place from the sad state it is in today, I knew an old photographer in my home town in Canada, who did all our family photos (on 4x5" ortho plates, and odd images they are to look at today, with our black lips and a death-like pallor on all his portraits. He processed all his films and prints in open trays with his hands. I recall his fingernails were black, obviously from some chemical in the home-brewed developers he brewed up - maybe pyro.
As almost everyone (except me) in those days, he smoked in his darkroom and being an old gentleman of very quirky personal hygienic habits, he would rinse out his stainless steel roll film tank under a hot water tap and then drink beer or whisky and ginger ale from it. For all his excesses he lived well into his eighties and eventually passed on from a severe stroke and by a fatal heart attack the next day, probably brought on by his sixty-year, two-pack a day cigarette habit.
Nobody paid much attention to matters like darkroom safely in those long ago days. When my dad built me a small home darkroom (in our linen cupboard at the top of the stairs) I had read an early Kodak darkroom guide and insisted on putting a small fan in the light-proofed window. On being told this the old gentleman pooh-pooed this as being so much airy-fairy gobbledegook, noting he had done very nicely for the past forty years of more... with all the windows sealed shut and then blacked out AND a kerosene heater he kept set on high in the cold months.
I think people were much tougher back then. I had proper clips (or tongs or whatever we called them then) for all my printing work - in fact I still have the original tongs I bought in 1958 - and very carefully washed my tank, trays, mixing jugs and bottles and anything that had come into contact with the chemistry I used then, in a laundry tub we had in our garage.
I've mixed some odd chemistry in my time - various dilutions of selenium and sepia toners, bleach and redevelop mixes, and an odd film developer I brewed up in the '90s from some obscure source to try and salvage 20 rolls of 50-year old Kodak film someone had and wanted the images rescued from if possible. This developer had sodium hydroxide in it, what for I've forgotten and I didn't keep any notes (now I wish I had, if only to satisfy my curiosity), and was really an effort to mix, as SH doesn't cope well with hot water and I had to add it to the mixed developer after it had cooled. Oddly, the films all came out and the client was happy, so it succeeded. That was probably my most adventurous project in the darkroom. These days I stay entirely with conventional chemistry, but I still clean carefully before and wash everything out carefully after a processing or printing session. That's just how I work.
I have always thought it pays to be careful, but it's also important to not overdo it, and above all not to overthink it too much.