Dust in homes is composed of about 20–50% dead skin cells. The rest […] is composed of small amounts of plant pollen, human hairs, animal fur, textile fibers, paper fibers, minerals from outdoor soil, burnt meteorite particles, and many other materials which may be found in the local environment.
Wikipedia says:
https://en.wikipedia.org/wiki/Dust
(I would know that there’s dead skin cells in there, because I’m allergic to dust mite poop. And dust mites feast on dead skin cells…)