Microorganisms in indoor air, such as bacteria and fungi, may pose a greater threat to respiratory health than previously thought, according to new research.
The research, led by Professor Wonsuck Yoon of Korea University, assessed lung toxicity in mice exposed to microorganisms typically found in indoor air. From these results they produced a risk assessment for human microbial inhalation.
The researchers collected microbial samples from over 500 busy indoor environments across South Korea, including restaurants, shopping centres and public transport stations. The most common microbes found were Staphylococcus (a bacteria) and Aspergillus (a fungus), consistent with findings from indoor spaces worldwide.
To assess health impacts, the team selected four representative microbial species – two bacteria and two fungi – and exposed mice to controlled doses of inactivated microbes over four weeks. While none of the microbes are typically harmful to healthy people, the mice showed clear signs of inflammation and lung damage.
Certain microbes commonly found in indoor air (such as M. osloensis, B. infantis, and B. adusta) triggered the release of cytokines, which are part of the body’s immune system response. When this happens in the lungs, it can lead to inflammation and tissue changes, similar to what is seen in conditions such as asthma and COPD.
This suggests that exposure to high levels of these microbes could increase the risk of developing or worsening these lung diseases, particularly in people who are more sensitive, like children, the elderly, or those with existing respiratory conditions.
Using these responses, the team estimated safe exposure limits for humans. Notably, they found that fungi could pose risks even at concentrations below current guidelines set by the World Health Organization and South Korea. Bacterial risks were more consistent with existing standards.
The research concludes: ‘Ultimately, our results emphasise the importance of establishing indoor microbial regulations based on toxicological evidence to enhance public environmental health by minimising potential risks associated with inhaling indoor air borne microorganisms.’
The full research can be read here.