Well, my poison ivy has abated, which is good news on several fronts. Besides the obvious one, it also means that I wasn't exhibiting a reaction to a particular reagent that I was using a lot of at the same time, an aryl isocyanate. Those are reactive little creatures, and they're known to bother some people. I'm very glad it wasn't an immune response to it, because (a) I still need to do reactions with the stuff and (b) I've never become sensitized to any lab reagent, and I'd hate to start now.
Probably the closest I've ever come was back in graduate school. I had a long synthesis that started with a tosylation reaction of a protected sugar. For the non-chemists, that's a way to convert an alcohol group into something much more reactive, and it uses a reagent called para-toluenesulfonyl chloride. Since even organic chemists don't like wandering around all day saying mouthfuls like that, it's abbreviated in the lingo as tosyl chloride.
And it reeks. It has a peculiar nasty sweetish smell, penetrating and hard to get out of your nose, particularly when you're crystallizing a kilo of the stuff. As I wrote in passing here, it was very easy to get fed up with that step. It got to the point that the smell gave me an instant headache, right up between the eyes. That's no longer the case, but I don't enjoy working with it to this day.
The other reagent that I couldn't take for a while isn't known as a sensitizer. When I was a teaching assistant during my first year, one of the sophomore organic labs was the preparation of phenyl Grignard reagent. They did that in good ol' diethyl ether, probably because it's cheap as dirt. Never mind that it's one of the most volatile (and flammable) solvents you can possibly use, and never mind that there were about two fume hoods for thirty students, so everyone just banged away out on the benchtops. The air practically got wavery with ether fumes, and why the whole place didn't go up is a real stumper.
I was teaching three lab sections a week that term, as fate would have it. After the first one, I had a headache from all that damned ether. That kicked in immediately during the second lab section the next afternoon, and I was really feeling awful by the end. Came the third section, and when the first gust of ether hit me I nearly hurled my lunch into the nearest sink. I just couldn't take it. I spent the whole afternoon teaching from out in the hall, asking people to hold up their flasks while I squinted at them and yelled encouraging advice. I only came into the lab to cruise from one side of the room to the other while holding my breath.
No, I couldn't take the smell of ether for a while after that one (it doesn't bother me now at all). But then, I spent my first week as an summer undergrad in Dale Boger's group (1982) surviving mostly on the contents of a jar of peanut butter, and it was a year or so before I could face that again, too. Academic chemistry does toughen you up.