Are you allergic to certain pet or pet product?

I am mildly alergic to my cats. My body aclimates to them, and I'm fine, but once in awhile I take in a new one and my head's a bit stuffy for a few days. Many people are fine while living with something but lose the resistance they built up when they don't live with it for a while. My Dad was fine growing up with cats in the house, but after they didn't have any for a while, his brother brought home a kitten and he started having asmacic attacks. I also find my cat allergy bothering me occationally when I am exposed to other things I'm alergic to, making me more sensative. In the Fall when there's lots of mold in the air, hanging at the Humane Society can make my head block up.