Cladosporium is a genus of mold that rarely produces lethal disease in humans except for causing skin and nail, sinus and lung infections. There are about forty individual species of Cladosporium, most of which are plant pathogens. When Cladosporium species spores are airborne, they can be allergens, and in large amounts might affect asthmatics, children, the elderly and individuals with respiratory disease or sensitivity. Cladosporium does not produce major mycotoxins, but the odor can be tied to volatile organic compounds, i.e. VOC. Species feed on dead herbaceous and woody plants, textiles, rubber, paper, food, floor, carpet and mattress dust, damp acrylic painted walls, wallpaper, drywall, HVAC insulation, filters and fans and wet insulation in mechanical cooling units. (Not a complete list.) This is a very common species of mold, found outdoors all year, with lesser concentrations in the winter. If the indoor concentration is not lower than the outdoor concentration, you probably need to do something about it.