Cat allergies are twice as common as dog allergies. But contrary to what you might think, it's not the fur or hair that's the real problem. People with cat allergies are really allergic to proteins in the cat's saliva, urine, and dander (dried flakes of skin).

How do these tiny proteins cause such a big allergic reaction in the body? People with allergies have oversensitive immune systems. Their bodies mistake harmless things -- like cat dander -- for dangerous invaders, and attack them as they would bacteria or viruses. The symptoms of the allergy are the side effects of your body's assault on the allergen, or trigger.

Keep in mind that even if you don't have an actual cat allergy, your cat can still indirectly cause your allergies to flare up. Outside cats can bring in pollen, mold, and other allergens on their fur.