I'll second that I couldn't beleive all those ruffty tufftys werent putting it on till I decided to do my own one day - BIG BIG mistake having a big pointy needle millimeters from soft tissue while you scream the house down.
We had giant bottles of it and it was used to stop bleeding, cure blisters (by drawing the moisture out of the skin causing it to harden sooner) and also as a decongestant when added to hot water.
they still use it in hospitals for sticking stubborn steristrips to cut up faces.
you could fill your blisters with surgical spirit but I wouldn't recomend it. best way is learn to avoid blisters and toughen your feet, tape em up or the US marine recon guys wear ladies nylon socks/tights under their normal ones to help cut the friction down.
It is still used (See www. BNF.org).
It is an Aromatic Inhalation, used to be called Friars Balsam, Tincture of Benzoin Compound.
How us Army types began putting it on blisters in the first place, I'll never know, on transfering to the Medics in the mid 70's, I was seconded to the then Para Depot Med Cen, where it was all the rage in the treatment of blisters. I never questioned (maybe I should have) why it was used, used to treat up to 20 pers a day, and most of them only needed one treatment, it got them through P coy, must have scarred them for life.
I'm sure there are ex paras on here could tell you more about the pain though.
I doubt if it's carciogenic as it would not be in the above mentioned literiture.