So, I decided to look it up online (LOVE the internet!) and let's just say, I was not thrilled with what I found!

From http://www.wisegeek.com/where-does-dust-come-from.htm

Outdoors, the atmosphere is filled with various kinds of dust, from windblown soil to pollutants. Ash from volcanoes, ocean salt, pollen and minute bits of decaying organic matter make up outdoor dust, which can circulate globally. The entire environment, from plants to animals, is constantly shedding dead cells. Industrial plants and vehicles add to particulate matter in the air, and seasonal fires add more ash.

Though the air in our homes appears clear and clean, unless you are using an air purifier or some other means of filtration, the air coming in from outside brings in a tremendous amount of dust. However, that’s just part of what makes up house dust.

It is estimated that humans lose 30,000 – 40,000 dead skin cells each and every minute. Furniture fabric, bedding, and clothes release fibers every time they are used or disturbed. Pets also contribute to house dust by shedding skin cells and hair. If your home is carpeted, there are even more fibers being released into the air.

YUCK!! I didn't need to see that just before lunch! But now I know I want to steam clean the whole house!!!