If you actually spent your life thinking about what might be on the poles or the escalator pads, or the seats or doors you would never use the tube, or any public transport.
There was a massive urban legend going round years and years ago about what was on the seats of tube trains, and so many people believed the truth of this email that the London Underground had to go on the radio to say it was bollox.
You would smell a rat though wouldn't you? Although that was the point as quite literally the remains of two large rats, 6 mice, an unheard of fungus plus lots of human deposits including urine and vomit were supposedly found on the seats.
You hardly ever see anyone feel the seat before sitting down, even travelling late at night when the likelihood of vomit and urine is a lot higher. The only times people do feel the seat is if a seat is suspiciously empty in a very crowded carriage.