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Air in 118 west London homes held more fungal diversity than the air outside
Between October 2022 and June 2024, passive samplers spent 28 days at a time in the living rooms of 118 west London homes. The fungal DNA they caught was more diverse than at four fixed outdoor sites, but this is a measurement of composition and burden, not of risk.
A baseline nobody had measured
On 4 June 2026 The Lancet Microbe published online a survey of the fungal DNA carried in the air of 118 homes in west London; it reached print in the July 2026 issue, volume 7, issue 7, article 101379. Samuel J Hemmings and Matthew C Fisher, both of the MRC Centre for Global Infectious Disease Analysis at Imperial College London, and their co-authors gathered 262 air samples — 222 indoors and 40 outdoors — recovered DNA from every one of them and assigned it to 2027 fungal genera. Read the paper.
Living-room air was richer on average than the outdoor air the team sampled: a mean of 646 amplicon sequence variants against 495 (p<0.0001), and Shannon diversity of 4.21 against 3.53 (p<0.0001). Composition differed sharply (permutational multivariate ANOVA, p<0.0001), with Penicillium, Aspergillus and Wallemia enriched indoors. Fungal burden across all the homes had a median of 11,043 genomic equivalents — the abstract prints the term as “genomic equivalence” — with an interquartile range of 4598 to 20,579 GE, from 28-day passive samples taken between 3 October 2022 and 14 June 2024.
What a passive sampler actually collects
The work belongs to the West London Healthy Home and Environment Study, or WellHome, an Imperial College London project co-designed with the local community in White City and funded by the UK Research and Innovation Strategic Priorities Fund Clean Air Programme. Households were recruited through community networks and partner organisations, from a range of socioeconomic backgrounds, with priority given to families whose children aged 5 to 17 have asthma or allergies. The 118 households held 504 residents: 263 women, 237 men and four not reported.
The 2025 WellHome protocol sets out two 28-day measurement periods in each home, three to six months apart. In the event, the paper reports, 104 households completed both campaigns and 14 completed one, which is where the 222 indoor samples come from.
Nothing was counted under a microscope. Material caught on the samplers went through ITS2 amplicon sequencing, and the quantity of fungal DNA was estimated by broad-range quantitative PCR targeting the 18S rRNA gene. A genomic equivalent is a converted count of genome copies: not a spore count, and not a dose anyone inhaled. Nor need a genus detected in a sample be growing in the room — the DNA may have come from dead cells, or arrived on shoes, or blown in through a window.
Four outdoor sites against 118 living rooms
Indoors versus outdoors does not mean each home against the air at its own door. The 222 indoor samples came from 118 living rooms; the 40 outdoor samples came from four fixed community sites across west London. The indoor set is more than five times larger, and amplicon richness climbs with the number of samples and the sequencing depth behind them, so part of the gap between 646 and 495 may follow from that imbalance. The abstract does not rule it out.
The 2027 genera are likewise a pooled total across all 262 samples rather than the contents of one sitting room. For scale, the 2024 outline of fungal classification accepts 10,685 fungal genera worldwide, so the London samples returned matches to roughly a fifth of them. That measures how far the sequencing reached, not what lives in a room.
What the result does not license
Greater diversity is not greater danger. The study measured composition and burden, and reports no health-outcome analysis, no risk estimate and no dose. The statement that long-term exposure to indoor fungal bioaerosols is a recognised risk factor for respiratory illness, particularly in damp and poorly ventilated housing, sits in the paper's Background and summarises earlier work rather than this study's findings. The household in which raised Aspergillus exposure was linked to repeated asthma hospitalisations in a sensitised resident remains a single observation inside an observational study, with no causal test behind it.
Seasonality needs the same care. Indoor communities showed stronger seasonal cycling (R² of 0.203) than outdoor ones (0.012), but R² is the share of variance a seasonal model explains, not the size of the swing. Nor does any of this transfer to British housing at large, still less to homes in general: this is a purposively recruited cohort in one part of London that deliberately over-sampled families with asthmatic and allergic children.
The one visible thread
The highest burdens were recorded in homes with visible mould, and that is the only part of the picture a resident can see unaided. Reaching the rest took a sampler standing for 28 days and a sequencer behind it. So the authors address policy rather than household habits: the paper offers no advice on ventilation, air cleaners or moving house, and asks instead that fungal bioaerosol monitoring be built into public health policy. The full structured abstract can be read without a subscription in the PubMed record. The article itself is harder to place — Crossref records the version of record as CC BY 4.0, while Europe PMC flags the same record as not open access — which is why this piece is illustrated with a public-domain photograph rather than a figure from the paper.
Written by MykoRadar from the source indicated. Informational only — it does not replace advice from an expert.