Can You Tell Me What Makes People Allergic To Cats And Why Not Dogs. What Is The Problem?

It is not cat fur to which most people are allergic, it is their dander.
Dander is a mixture of a cat's hair, saliva, and minute particles of skin. A cat owner's home will be covered in an invisible layer of dander, deposited by the finicky creature's constant self-grooming.
Allergy to cats affects more children than adullts. Children may grow out of their reaction so some allergists suggest desperate parents try turning the offending animal over to a relative or friend for three months.
To rid a house of dander, you must have it professionally cleaned, including shampooing all upholstered furniture and the carpets and washing all bed linens. But, as the old song says, "The cat [dander] came back the very next day ..."
Some brave souls actually bathe their cats regularly in order to control dander.

I'm allergic to dogs - don't be stupid /=(