How do cat allergies work?

[DanielK]

If someone is allergic to cats, would they be allergic to every cat they come across, or does it just depend on the cat?
I've recently took in a stray cat, and it's been giving me minor allergy symptoms. However, I've been around a lot of cats & dogs before (including strays) and I've never had this problem before.

 

[diddy]

cat allergies are because your allergic to the cat saliva, so if the cat sheds a lot that will make you have more allergies because more hairs with their saliva on it is floating around. also it could be because its spring and the change in season makes animals shed more.