Various yeasts are commonly identified on air samples. Some yeasts are reported to be allergenic. They may cause problems if a person has had previous exposure and developed a hypersensitivity. Yeasts may be allergenic to susceptible individuals when present in sufficient concentrations.
"Aw" refers to the water activity measurement, where Aw is equal to the relative humidity of the air surrounding the sample when the air and the sample are at equilibrium (in an enclosed space).