What gives thrift stores that unique smell?

I find that all thrift stores tend to smell exactly the same, but I can't pinpoint what gives them that trademark smell. I'm used to my clothes either smelling like detergent, fabric softener, or my cologne. So I have no idea what all contributes to the stench of raw thrift store items. I'm guessing it's a mix of B.O., mildew, moth, and other things. Anyone know an exact formula?