Airborne particles are a major cause of respiratory ailments of humans, causing allergies, asthma, and pathogenic infections of the respiratory tract. Indoor fungal charge can contribute to development of sick building syndrome or other building related illnesses and often some people can have an allergic response. Such indoor exposure to moulds and their spores is unavoidable except when the most stringent air filtration or other environmental measures are observed. The repeated exposure to large amount of particular fungal propagules is an important risk factor for the development of specific allergic reactions. There are also a large number of toxic mould metabolites which can have a range of biological activities but there is no information at this time on the effects of chronic, low dose inhalation exposure to mycotoxins. A relevant issue is determining which cognitive functions make humans to attribute their health problems to environmental factors and how individuals with proved environmental health problems can perceive that as a biological stress indicator. All tipes of moulds can produce large numbers of spores that can be inhaled and some of those are small enough to be respirable by occupants and deposited on the mucosal surface of the upper airways or in the eyes, sometimes inducing hypersensitivity pneumonitis or causing much worse health problems. Regular detection, quantification and characterization of moulds in living and working environments are essential for exposure risk assessment to safe guard public health.