When you guys said "unhygienic" and "infection", my first thought was๏ปฟ
of germs and bacteria, which are microscopic. When you said "bugs in
the mattress", I think of bed bugs, which are not microscopic - I looked
it up. Most things microscopic would be able to slip through the fibers
of the sheet. Things that are not microscopic, probably would not fit
through the sheet fibers.
So, if you're talking about bed bugs, Amy you're probably right, although
they can still crawl out from under the sheet to get to that warm body
they're looking for. As for things microscopic, a sheet most likely won't
offer much protection.
For wetness, however, a sheet gives no protection, at all. The mattress
is going to get wet, almost guaranteed, unless there's something water-
proof under the sheet. And along with the wetness, goes anything micro-
scopic.