Here's the thought pattern you have to fight, and people are not going to say this to you as clearly as I will, because of taboos:
Where does the dirt, dust (human skin flakes, semen, lube, dingleberries, etc.) go? I'm sorry for going into ugly stuff but you need to hear it.
I don't think people are going to buy into this mentally, which leads me to think they aren't going to buy it with their dollars, either.
Also don't assume that having an answer for this concern removes the concern as a problem for your business. You may have an answer, but people need to buy your answer.