Could undetectable micro black holes floating around the universe cause cellular damage if they passed through a person's body? What is to say there are not trillions upon trillions of micro black holes floating around Earth passing in and out and occasionally swallowing parts of cells of people, animals, plants, and other things?
Is this a possibility? Why or why not? Just curious.
 A: No, it is not a possibility. I don't say this to cast doubt on the existence of micro black holes, but rather because of their properties.
Black holes evaporate via a process known as Hawking radiation. This means that, in theory, every black hole should eventually evaporate completely, and disappear. For micro black holes, this would be very important. Any micro black hole would evaporate incredibly quickly, too quickly to do any damage to anything. The possibility of micro black holes destroying objects around them has been discussed quite a lot, albeit in the context of "safety concerns" regarding particle accelerators, but that possibility is negligible. https://en.wikipedia.org/wiki/Safety_of_high-energy_particle_collision_experiments gives a brief discourse on those arguments.
Another argument against the existence of all those micro black holes is that there is no reasonable source for them. Without going into detail about the formation of any theorized micro black holes, I can say that there is no mechanism that would explain the formation of trillions of micro black holes. If they don't form in such quantities (or at all) in the first place, we don't have to worry about how they would disappear. 
