Hi! I am allergic to cats, I guess thats why i like dogs more haha. 
Do you have the most common allergy that comes from a cat's saliva? 
I'm not sure. Sometimes when I touch a cat, I sneeze there-after.
That is an allergic reaction called a histamine reaction.
Wow! Is it common among people?
I'm not sure, in some people, they are so allergic, it causes the person's airway to close up and they need emergency medical attention!
Wow! Yes I know people who have to go to the hospital for allergies.
There isn't a lot of public awareness for people with the severe allergy, it's a shame it's not more talked about like food allergies.