Allergy to cats is quite common and results in a streaming nose and eyes and sometimes in wheezing. The allergy is to one or more proteins that cats produce - especially in their saliva. When washing themselves, this is transferred to their fur; once the protein has dried out it can become airborne.
In Latin, the house cat is known as Felis domesticus. The most important cat allergen is termed Fel d1. It is carried on very fine particles which can be found in the air of most homes, even those where there is no cat. The same particles can be found on clothing, on soft furnishings in the home and even on bus and cinema seats. Because the particles are very fine, they remain suspended in the air for a long time; people with allergies to cats often get symptoms within minutes of going into a room where a cat has been. If a cat is removed from a home - for one reason or another - it takes around six months for the allergen to disappear completely.
You come into contact with these microscopic particles every day. And once they're on your skin or inside your airway, the allergens run into a group of specialized cells and organs, called the immune system. The cells in this system search out and destroy any microbe that could be dangerous to the body. A nonallergic person's immune system recognizes that allergens are harm less--they do not cause disease--and ignores them.

But when an allergic person comes into contact with an allergen, such as Fel d1, their immune system has a different response. They may sneeze, get a rash, or even have breathing difficulties. "An allergic person's body is attempting to protect them from something it really doesn't need to," But having allergies isn't a sign of a faulty immune system. If anything, it means the body's immune system works too well, like an over-protective bodyguard.
When an allergy-prone person is first exposed to an allergen, such as a cat's, their immune system produces millions of IgE anti-bodies. These Y-shaped molecules are trained to recognize a specific allergen and alert the body's defenses. A person who is allergic to cats has a stockpile of anti-bodies specific to cat allergens. Someone who isn't allergic to furry felines does not make as many IgE antibodies. "If someone is allergic to cats you can measure the antibodies against cats in their blood with a skin test. . "The more allergic antibodies in the person's blood, the greater is the likelihood that the person will have an allergic reaction when they meet a cat."
Did You Know?
* Scientists think that cats may use their Fel d1 proteins as a scent marker--male cats produce more of the protein than female cats.
* Why would the immune system attack a harmless particle? Scientists hypothesize that the part of the immune system that responds to allergens originally evolved to protect people against deadly parasitic worms. "Nowadays we don't have a lot of these parasites around," says allergist Steven Kernerman. But the proteins on parasites recognized by the immune system look similar to what's recognized on the allergen.