Odor of slippers

The smell of slippers.......Almost impossible to be good,especially those are used.Yes I tried to smell my slippers,most of the odor is the smell of rubber,while mix other smells such as sweat and body odor.And,different parts emit different kinds of odors.For example the parts which contact with heel are stronger than other parts,I think because we put more pressure with heels on these parts.As for the bottom of slippers smell stuffy---I think this is strange because you can feel this even with your eyes closed,they are stuffy.It's difficult to explain that because it is the dirtiest part full of dust and dirt,but it really smells a "black" smell.