West Epoxy is 5 to 1 which means the hardeners are more reactionary.

System Three and some others are 2 to 1 and less likely to effect you.

Rob

I have a chemistry background, and I don't think this makes a lot of sense. You could just as easily (and equally questionably) say that because there's 'less' hardener in the WEST mixed epoxy, it's less dangerous/sensitizing.

I think that the differences in epoxies with regard to sensitization and allergies are more of a question of the identity of the chemicals and their volatility and ability to penetrate the outer (dead) skin layers. I've never worn a respirator using epoxy but like Bill Hamm, I am very diligent about avoiding skin contact and immediately wash any suspected contact areas with vinegar and lots of water, and then soap. So far (35 years in), no problems.
However, if asked, I always say that it's safer to use a good respirator when using any organic compounds. (So, don't contact your lawyer just yet..... ;-)

I avoid the more 'smelly' epoxies, but that's meaningless since some odorless chemicals are really dangerous.

I've used WEST epoxy mostly and there are definitely differences between products. I used one jug of EAST epoxy (a Canadian knockoff of WEST) years ago and it was way more smelly than WEST, as was ColdCure. I'm more suspicious of volatile mixtures. It was EAST epoxy that an acquaintance was using when he became so sensitized to all epoxies that he had to stop working on his (big_ sailboat project. Fortunately, he could afford to hire a boatbuilding crew, but he couldn' even go in the boat shed where they were working without having respiratory distress and eyes swelling.