Well, from what I learned when my cats had problems from carrageenan was that the reaction carrageenan caused for them was not a true allergic reaction. Basically, among many other problems carrageenan can cause digestive problems, and it can also have an inflammatory effect. Carrageenan causes digestive problems because it inhibits pepsin and other gastric enzymes. It depresses peptic activity. In a human the result can be a stomach ache. In cats, vomiting. In fact, in some cats, the digestive problems from carrageenan can be so severe that the cat can't digest/keep down any food. (None of my cats ever had any other reactions from carrageenan, so I don't know what else it could cause for them.)
Anyway......My bad experiences with carrageenan go way, way back. All the way to the fall of '86, when the manufacturer of the canned cat food we were buying switched from guar gum to carrageenan, and suddenly we had a sick cat. Long story short, vet found nothing that could have explained what was going on with him, so we decided to check things on the fancy new label that was telling us that the food was now "improved". When we compared the ingredients in the old formula and the "improved" one, we found only one difference. All the ingredients were the same, except now, instead of guar gum, the food was thickened with carrageenan.
Luckily there was some info about carrageenan in one of our books. And it explained what was going on with our cat. I think, that problem was the easiest problem to solve, ever. So simple. All I had to do was go out and find food that was not thickened with carrageenan.
I'll PM you the info I have in the book, so you can read it all. No web link, so I can't post it.
Info from the webhttp://www.notmilk.com/carageenan.htmlhttp://www.wisegeek.com/what-is-carrageenan.htm
Very interesting posts here, including people's experiences with allergic reactions. Also some info about allergy testing.