Well, my feet are filthy when I take off my shoes.
In dusty conditions, I will take shoes and socks off at breaks and beat the dust out of my socks, and wipe my feet off with them, then put them back on.
Its just foot maintenance.
Sometimes, my shoes have been so full of dirt it sort of feels like walking in sand at the beach, you know there is dirt between your toes, etc. But there really isnt much there, just a bit.