The occupants of a building can be adversely affected by low moisture levels. Similarly, when moisture levels are too high, discomfort and irritation of the mucous membranes, as well as a 'skin-wetness' or sticky feeling can occur.
High moisture content on surfaces can also cause microorganisms to propagate. Microorganisms growing indoors, such as fungi and bacteria, are capable of producing metabolites, protein, and polysaccharide structures that are possibly toxic, inflammatory, or irritating, depending on individual sensitivities and genetic predisposition.