The ISS is a pretty messy place, as in the image here. I have a cable mess under my desk that quickly traps dust and takes some effort to be cleaned. The ISS is much worse. And it has been crewed constantly since November 2000, by almost 100 persons now.
I suppose the ventilation and its filters takes care of some of the dust, and I can imagine that it is more efficient as a kind of vacuum cleaner in microgravity. But humans have fatty sticky skin and hair that falls off. And there's alot of mixed materials exhaled, we exhale about as much water as we deposit in toilettes. The crew cannot walk but has to grab things with their hands in order to move. Door handles and even light switches in unclean homes are disgustingly tainted by filth because they are often touched.
What cleaning equipment, chemicals and routines are used on the ISS and how much time is spent on cleaning? Spray bottles with detergents might not be a good idea in microgravity since it would end up everywhere, including in the lungs and on the skin of the crew. Swabbing the floor isn't even possible. I don't see images of the crew using hair nets and gloves much, shouldn't the ISS be treated a bit like a clean room?
Is filth an important problem as in threatening the astronauts' health or restricting the life time of the hardware and the station itself?
Columbus laboratory on the ISS.