What is dander? According to Wikipedia (my new bible), "dander is material shed from the body of various animals, similar to dandruff or pet pollen. It may contain scales of dried skin and hair, or feathers. It is a frequent cause of allergies in humans." Contrary to popular belief, pet hair is not what causes allergies; it's dander, i.e. the dead skin that flakes off of the body of animals. Dander is usually very small, fluffy and cannot be seen by the naked eye. It spreads throughout the atmosphere and gets transported on virtually everything.
Dander particles shed from pets can stay airborne for hours, and in the case of cats, for months. The allergens in dander stick to clothing, and remain in carpets, mattresses and furniture even with meticulous cleaning. Therefore, someone with pet allergies can suffer from symptoms for months, despite pets having been removed from the home. In many cases, it's the person who has to abandon the place. Obviously, that new daycare is no longer an option for us - cat stays, Maya goes.
With cats, it's even more of a problem because cat dander is not only in their fur, but also their saliva and urine. How does a cat clean itself? Yes, you got it. It licks itself clean and then jumps on your sofa, leaving all that residue of sticky saliva and dander together. Your allergic child decides to sit on the sofa, and moments later, itches at her eyes and sneezes.
Anti-histamine to the rescue...