I can attest to the fact that yes dirt, hair, fabric softeners do build up inside a dryer. We were selling a very good name brand set of washer and dryer and I simply could not let anyone else see our 'dirt'. Scrubbing the outside of the machines wasn't enough for me, so of course I had to take off the holder for the lint trap. Checking the gasket that was underneath the it, we found actual sandy, black dirt and pet hairs (2 dogs, one cat over the years). It was dried on hard. Also, something at one time had gone through the pockets in the wash and survived getting to our new dryer. It stuck to the tumbling blades inside the dryer, right where the blade and the drum are attached. Over time, things have also attached themselves to it. So yes, dirt can be released inside the dryer.