I think it's a phobia rather than an allergy. There's a Mary Stewart novel set somewhere near Beirut (it's the ULTIMATE Gothic girl-meets-house novel, given the house in question is part crusader castle, part middle-eastern pasha's retreat complete with harems and secret passages and an indoor lake) where the girl's cousin works out that their mad great aunt who thinks she's the reincarnation of Lady Hester Stanhope is in fact dead and being impersonated by her drug-smuggling personal physician because there's a cat in the room and both the protagonist and her mad great-aunt are severely cat-phobic.