The air inside UK homes contains a greater diversity of fungi than the air outside, according to a major new study that could have important implications for public health and housing policy.
Researchers at Imperial College London have carried out the UK’s largest long-term study into indoor fungal air pollution as part of the WellHome study.
The study, which concentrated on children with asthma or allergies, as well as families from ethnic minority groups and lower-income backgrounds, tracked air quality in 118 households over two years.
This particular element of the research analysed airborne fungal communities in those homes over a 20-month period, in what is believed to be the first large-scale UK investigation of indoor fungal bioaerosols.
The team collected 262 air samples from the homes and outdoor locations between October 2022 and June 2024, identifying more than 2,000 fungal genera. Using DNA sequencing techniques, they found that indoor environments contained significantly richer and more varied fungal communities than outdoor air.
Rather than outdoor air being the primary source of fungal exposure, it was found that homes create complex environments where building materials, furnishings, moisture levels and everyday activities contribute to unique fungal ecosystems.
Several fungal groups, including Penicillium, Aspergillus and Wallemia, were found in greater abundance indoors than outdoors. Many of these fungi are associated with damp conditions, respiratory illnesses and allergic reactions.
The study also revealed that indoor fungal communities changed significantly throughout the year, with some species becoming more common during summer and others peaking in winter and early spring, whereas outdoor fungal communities remained relatively stable across the seasons.
While most fungal exposure is harmless, prolonged exposure to elevated levels of airborne fungi has been linked to asthma, allergies and other respiratory conditions, particularly among vulnerable individuals.
Predictably, properties with visible mould generally recorded some of the highest fungal levels but one of the most striking findings involved a household with no visible signs of mould but unusually high levels of Aspergillus spores.
The home was occupied by a child with an allergy to the fungus and a history of asthma-related hospital admissions.
Samuel Hemmings, PhD student in Imperial’s School of Public Health said: ‘This research demonstrates that [visual inspection] methods alone are not sufficient in detecting the true burden of fungal bioaerosols within homes.’
Professor Matthew Fisher, Professor of Fungal Disease Epidemiology at Imperial, added: ‘These findings prove that fungal aerosols are an important but often overlooked component of indoor air pollution. Integrating fungal monitoring into housing and public health policy is now vital for improving respiratory health in the UK.’
The findings come amid growing concern about the health impacts of damp and mould in housing, particularly following the introduction of Awaab’s law which is aimed at improving standards in rented accommodation.
The full research can be read here.
Photo: masakazu sasaki
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