In many cases the building itself is too damaged to recover, as the materials themselves (wood structural members) are decaying from mold or rot. The phenomenon is found worldwide in buildings with lower than adequate maintenance or other economic concerns. Some health professionals recommend anyone living in an older building with medical conditions, to use HEPA air filters for indoor use to minimize airborne particulate introduced from outside the living space. Some symptoms are linked to the average amount of time spent in a building, such as mold spore and dust inhalation.