Cats, dogs, horses, and other mammals produce proteins in their skin that can cause allergic symptoms. These allergenic proteins are present on tiny microscopic particles. Because of their very small size (much smaller than pollen grains or dust mite particles) they easily become airborne, and remain suspended in the air for long periods of time. Contact of these particles with the eyes, nose, or bronchial tubes can then provoke an allergic reaction.

Although it was previously thought that the allergens originated in the animal's saliva and were only transferred to their skin, it is now known that the allergens are produced in the skin itself. It is not the hair of the animal, but rather the dander produced by the skin, that causes the allergic reaction. There is therefore no truth to the common statement that a non-shedding pet is not allergenic. Even a non-shedding pet produces dander, so the sad truth is that there is no such thing as a non-allergenic breed of cat or dog.

However, it is true that just as some individual humans have more dandruff than other humans, so do some individual cats or dogs produce more allergenic dander than other individual cats or dogs. Female and neutered male cats produce less dander than un-neutered males, but these amounts are still sufficient to provoke allergy symptoms.

WHERE ARE ANIMAL ALLERGENS FOUND?
Animal allergens are of course found mostly in homes where pets are present. What is surprising, however, is that these allergens are also found (in lesser amounts) in places where pets have never been present, such as schools, workplaces, and other public spaces. Animal allergen is brought to these places on the clothing of pet owners. Dander allergens are sticky, and they adhere to other surfaces. Dander on a smooth surface, such as a wall, can be easily wiped off, but dander in soft materials, such as carpets, mattresses, upholstered furniture, and clothing, can persist in that fabric for long periods of time. That is why, unless special steps are taken, pet dander can remain in a home for up to six months after the pet has been removed.