The most common behavior problem reported by pet parents of cats is inappropriate elimination. It’s estimated that 10% of all cats will eliminate outside their litter box at some point in their lives. Quite a few of these cats have issues with some characteristic of their litter box (please see our article on Litter Box Problems for more information on litter box problems), but approximately 30% don’t have litter box problems at all. These cats are urine marking, and urine marking isn’t a litter...
The short answer is scientists don't know. If you have allergies and want a cat, it may be possible to find one that won't bother you. But experts can't explain why.
Anatomy of an Allergy
People with cat allergies react to a protein in the animal's saliva, skin, and urine. The allergen collects on the cat's fur when the animal licks itself and comes off in tiny flakes of skin that glom onto walls, carpet, and furniture or stay in the air. A cat's lick or scratch can cause skin welts or itchiness. In the nose and lungs, the protein causes itchy, watery eyes and nasal congestion and can lead to asthma.
The allergens are so powerful that they can hang around for months, causing effects long after the cat is gone.
Some cats secrete less of the protein, some cats put out less saliva, and some cats produce less dander. But all cats make the allergen in some form -- and a tiny amount can cause a lot of symptoms, depending on how clean you keep your house and how often you're around the animal, says Robert Zuckerman, MD, an allergy and asthma specialist in Harrisburg, Pa.
"Even a cat that has a little bit of allergen can cause allergy if you have enough exposure to it," Zuckerman says.
The other variable is your immune system. Maeve O'Connor, MD, an allergy, asthma, and clinical immunologist in Charlotte, N.C., says one person can hold a cat and have no symptoms, while another has an asthma attack standing near a person with cat dander on his or her clothes.