Like SoulsMom, I'm allergic to everything except food - seriously! Depending on which school of thought your Dr prefers, either dander or a component in the saliva (more appropriate for the self-cleaning cat) that causes the majority of reactions. CLEAN is the operative word, both for the environment and the dogs. I have 3 cats and 3 dogs and there was a time that I couldn't even walk into a home where a cat resided, let alone live with one!
Oh, and since I can't take Zyrtec unless I need to sleep for 2 days, I rely on the non-drowsy generic version of Claritin during the time that my other allergies are kicking up, and TylenolPM (with generic benadryl as the sleepy component) to keep things in check the rest of the time and get a good night's sleep. Everyone has to find what works for their individual situation/sensitivity. Good luck!