I became sensitive about half way into my build. After that I had to wear a full suit, double gloves, hood, and repirator just to mix small amounts. I also found out that the mixing ratios make a difference. I tried one with 100:16 ratio and it was much worse than the 100:25 I had been using. A noticeable difference. I didn't have a lung problem, but my arms, hands, and neck would break out terribly as soon as I got near the epoxy. After staying covered up for two years, now I can do small amounts without it bothering me, as long as I don't get it on my skin.