Fungi are found throughout the environment, including the air. Outdoors, there is about one fungal spore per liter and we breathe ca. 11,000 liters of air each day. Outdoors, therefore, you breathe in ca. 11,000 spores each day. Buildings reduce the amount of fungi and, in a well-constructed and maintained building, you would breathe in only ca. 1,100 spores/day. In a water damaged building, where fungi grow on wall board, paper, paint, glue, caulk and wood, the concentration of spores can rise by 10- to 100-fold or more. In these buildings, you could breathe in 110,000 or more spores/day.