Damp and mould are linked to asthma. The fix is the moisture, not the bleach

Living in a damp or mouldy home is associated with a higher risk of respiratory symptoms, asthma and infections, and the intervention the evidence supports is controlling the moisture rather than identifying which mould is present [s1][s2]. The World Health Organization's 2009 review of indoor dampness and mould concluded there is sufficient epidemiological evidence to link the conditions in buildings to respiratory effects including cough, wheeze, upper-respiratory symptoms and the exacerbation of asthma [s1]. An earlier Institute of Medicine assessment reached the same broad conclusion for asthma symptoms and other respiratory outcomes [s3].

The strongest quantitative summary of the infection link comes from a 2010 meta-analysis pooling studies that adjusted for major confounders [s2]. It found that residential dampness and mould were associated with an odds ratio of 1.45 (95% confidence interval 1.32 to 1.59) for bronchitis and 1.44 (95% CI 1.31 to 1.59) for respiratory infections [s2]. Those are moderate increases — on the order of 40% higher odds — and they were statistically significant and consistent across the included studies [s2].

Why the water matters more than the species

A recurring theme in the agency reviews is that the health signal tracks dampness itself, not any single organism [s1][s3]. Damp materials support not only visible mould but bacteria, dust mites and chemical emissions from decaying building materials, and studies have not isolated one causal agent [s1]. That is why WHO framed its recommendation around persistent dampness and microbial growth as the target, and why routine testing to identify mould species is not considered clinically useful for deciding what to do [s1]. If there is visible mould or a damp smell, the response is the same regardless of what a lab culture would show: find and stop the water [s1].

Practically, that means fixing leaks and condensation, improving ventilation in kitchens and bathrooms, and drying water-damaged materials quickly — porous items that stay wet are often discarded because they cannot be reliably cleaned [s1][s3]. Bleaching a surface removes the visible stain but does nothing about the underlying moisture that will regrow it [s1].

The limits of the evidence

The associations are drawn from observational studies, which cannot fully separate dampness from the older, lower-income or more crowded housing where it is more common, and the reviews are careful to describe the evidence as sufficient for association rather than proof of causation for every outcome [s1][s2][s3]. The effect sizes are moderate, not dramatic — a home being damp raises risk, it does not guarantee illness [s2]. And the studies rarely demonstrate that a specific remediation prevents a specific case, because that trial is hard to run [s1].

What holds across all three authoritative reviews is the direction and the action: indoor dampness and mould are linked to worse respiratory health, the harm is preventable, and moisture control — not mould testing or surface disinfection — is the evidence-based response [s1][s2][s3]. This is an informational summary and not medical or home-remediation advice.