Initial studies did not show any relationship between moulds/damp and health, as there was major confounding with socioeconomic status, and because it is hard to quantify mould exposure (with many different mould species).
Then there is the effect of climate, and the built environment – heating, ventilation, insulation, materials etc.
More recently systemic reviews have made it clear there is a link particularly with development of asthma, particularly in older children, and where there is already a family history of atopy.
Longitudinal studies have suggested that there may be protective effects but data is limited.
Similarly there is evidence that higher exposure to moulds leads to more asthma exacerbations.
There are genetic polymorphisms that affect ability to break down the fungal protein chitin, and these have been linked to urgent medical care visits, which suggests a non-immune mechanism may be important.
Dampness is linked to mould growth but also to house dust mite, microbial volatile compounds, mycotoxins and endotoxin.
The most studied mould species are Aspergillus, Penicillium, Alternaria and Cladosporium.
Limited evidence that interventions to reduce mould make any difference.[European respiratory review 2018]