Introduction. The article provides a rationale for the methods of detection, criteria, and indices for assessing the health hazard for the population from contamination of air and wall structures of premises with permanent human presence by microscopic fungi.

Materials and methods. An analysis of domestic and foreign scientific reports and regulatory and methodological documents on the issue of assessing and regulating pollution of the indoor environment by microscopic fungi was carried out. A comparative assessment of the content of fungal flora in apartments of healthy individuals and individuals with allergy pathology was carried out, as well as an analysis of the results of population surveys using invasive and non-invasive research methods.

Results. Based on the analysis of scientific literature data and own research, there was made an assessment of the impact of various levels of microscopic fungi in indoor air on the health of residents. It was shown that with a mold concentration below 500 CFU/m³, the presence of visible fungal infection was not detected, and no effect on health was established. In the presence of visible foci of fungal infection of more than 5% of the total area of ​​​​the walls, floor, ceiling, the content of microscopic fungi in the air exceeds 1000 CFU/m³, in previous studies, with a mold content in the air over 1500 CFU/m³, an increase in the level of specific IgE in the blood serum in children was previously established, and in allergy sufferers, an exacerbation of allergic reponses is possible. When the content of microscopic fungi in the air is above 2000 CFU/m³ in the premises, there are lesions of more than 10% of the surface area of ​​enclosing structures, a reliable increase in allergic pathology and a reliable change in the cytological indices of the mucous membranes of the mouth and nose are noted.

Limitations. The results of this study do not apply to premises of livestock and poultry complexes, as well as biological industry enterprises.

Conclusion. The concentration of microscopic fungi in indoor air, not exceeding 500 CFU per 1 m³, can be considered as an acceptable level of their total content in the air of premises with constant occupancy. This concentration corresponds to the content of fungal spores in the atmospheric air, indicates to the absence of foci of fungal infection of wall structures, should not cause the development of allergic responses in healthy individuals and is consistent with WHO recommendations on the standardization of this factor.

Compliance with ethical standards. The study does not require the submission of a biomedical ethics committee opinion or other documents.

Contributions: Kalinina N.V. — concept and design of the study; data collection and processing, text writing; Slobodyan V.G. — editing; Starodubova N.Yu. — concept and design of the study; Gaponova E.B. — data collection and processing; Banin I.M. — data collection and processing, statistical processing. All authors are responsible for the integrity of all parts of the manuscript and approval of the manuscript final version.

Conflict of interest. The authors declare no conflict of interest.

Acknowledgement. The study had no sponsorship.

Received: July 5, 2024 / Revised: August 7, 2024 / Accepted: October 2, 2024 / Published: November 19, 2024