| Hi Lorraine,
having done a bit of research I suggest that you take care what you give your cat, as they are very sensitive to most remedies, including herbal ones (essential oils). Some people suggest a mixture of Borax powder and hydrogen peroxide, but then again it might be more prudent to find out what your cat is allergic to and then eliminating that allergen, if possible.
That being said, I am supposing that it's not the food your cat eats, so it' probably somewhere in the environment around the house (?). Perhaps it would be a good idea to have a look at http://www.petsfortheenvironment.org/blog/ as they seem to be in the natural side of pet care.
Leo |