Where the dust actually goes

What is actually happening

The grit fraction is the one worth understanding, because it is the only part that is abrasive. It is angular mineral, and loose grit falls to the base of the pile where it sits below the wear surface and does comparatively little. Grit landing on an oily fibre does not fall. It sticks at the top, exactly where every footstep presses it into the yarn, and from there it files at the fibre like sandpaper held against it. That is the difference between dust a carpet carries harmlessly and dust that costs you the carpet: not how much there is, but whether the pile is oily enough to hold it at the surface.

How you prevent it

Vacuum slowly. Fast passes ride over grit rather than lifting it, and slow passes on the traffic lanes are worth more than frequent quick ones. Vacuum the bare mattress each time the sheets come off, which is the one moment the surface is accessible and takes about a minute. Then have the oils extracted on a real cycle, because once the oils are gone the grit has nothing to hold it at the top and falls to where it does no damage. Spiker measures none of this on a residential job — the mechanism is checkable, an outcome is not.

Most of it settles into the surfaces people spend the most uninterrupted hours pressed against — mattresses and soft furniture more than the floor — and the rest works its way down into the carpet pile. Dust is not one substance. It is skin and fibre and, the part that matters to a carpet, mineral grit walked in from outside.