Mold growth in buildings generally occurs as fungi colonize porous building materials, such as wood. Many building products commonly incorporate paper, wood products, or solid wood members, such as paper-covered drywall, wood cabinets, and insulation. Interior mold colonization can lead to a variety of health problems as microscopic airborne reproductive spores, analogous to tree pollen, are inhaled by building occupants. High quantities of indoor airborne spores as compared to exterior conditions are strongly suggestive of indoor mold growth. Determination of airborne spore counts is accomplished by way of an air sample, in which a specialized pump with a known flow rate is operated for a known period of time. To account for background levels, air samples should be drawn from the affected area, a control area, and the exterior.