Any decomposing material or rotting food within the clutter could attract rodents and pests, which can then start to build their communities and remain hidden among all the hoarded items. These pests can be biohazardous, often carriers of multiple diseases. Besides this, during the hoarding cleanup, you may have to deal with removing them (dead or alive) and cleaning up their urine, feces, and any other bodily fluids, which are serious biohazards.
Sometimes, a hoarder’s compulsion includes hoarding animals, which makes the issue that much more sensitive. Animal hoarding can be extremely unhealthy and dangerous for the animals and the people living in the same space. Feces, urine, and any other filth put all the living things at risk. Attempting a hoarding cleanup when there are biohazards involved can make the task much more dangerous as you could be exposing yourself to bacteria, viruses, and other pathogens.