I am extremely allergic to cats, and have been hospitalized a couple times for reactions. (If you read the Marriott thread, I swear it's only cats and down feathers - same type of reaction to both, but nothing else.) The biggest issue is I need to be careful about the cat hair getting in my eyes. Maybe three years ago, there was a woman in the waiting area with a cat in a soft sided carrier. I asked the GA to check to be sure the cat wasn't going to be under my seat. Of course, it was. She offered to move me, but couldn't move my seat mate, so the woman with the cat was moved to the back. The woman with the cat was a little peeved, but the GA explained that it was that or not on the flight, and the woman calmed down.