The science is in: how mould in your home actually affects your health

If you've ever spotted that black speckling creeping along your bathroom ceiling or behind the wardrobe, you've probably wondered whether it's actually a health issue or just a cosmetic one. The honest answer, after years of running Dew Moisture and reading the research that keeps landing on my desk: it's a real health issue. And the evidence is no longer up for debate.

What the World Health Organization concluded

Back in 2009, the WHO published its first global guidelines on indoor air quality, focused specifically on dampness and mould. After a two-year review by 36 experts worldwide, they came to a striking conclusion: people living in damp or mouldy buildings have up to a 75% greater risk of respiratory symptoms and asthma compared with people in dry homes. That figure alone reframed indoor mould from a property issue to a public health one.

Their core recommendation was almost embarrassingly simple — prevent persistent dampness, and you prevent most of the health risk. We'll come back to that, because it's the entire reason Dew Moisture exists.

The respiratory effects we now know are real

A large body of meta-analyses (which pool results from many quality studies) consistently link visible mould or mould odour in homes with measurable increases in:

• Asthma development and asthma flare-ups
• Wheeze, cough and shortness of breath
• Upper respiratory tract symptoms (think stuffy noses, sinus issues)
• Bronchitis and respiratory infections
• Allergic rhinitis (hay-fever-style symptoms)
• Eczema flares

Researchers at Lawrence Berkeley National Laboratory have estimated these effects translate to roughly 30–70% increases in the prevalence of those health problems in homes with dampness and mould. In the US alone, the annual health-related cost of dampness and mould has been estimated in the billions — around $17 billion for asthma morbidity and mortality, with separate billion-dollar figures for allergic rhinitis and bronchitis.

It's not just severe mould

One of the most useful things about the modern research is that you don't need a dramatic, wall-blackening mould outbreak to be affected. Studies use surprisingly low-tech indicators — visible mould, mould odour, a history of water damage — and still find significant health associations. A musty smell that lingers in a bedroom or a slowly creeping patch behind the curtains is enough to nudge the numbers.

Who is most at risk?

Healthy adults can usually tolerate moderate exposure, but the research is consistent about who suffers most:

• Babies and young children, whose airways are still developing
• People with existing asthma or allergies
• Older adults
• Anyone immunocompromised — including people on certain medications or going through cancer treatment

If anyone in your household falls into one of these groups, the case for taking dampness seriously gets a lot stronger.

The good news

The same studies that document the risks also document the upside of fixing it. Adult dampness remediation has been associated with roughly a 40% reduction in respiratory and asthma outcomes — including medication use. In other words, getting moisture and mould under control isn't just preventative. It can actively improve how people feel and breathe, often within weeks.

That's the part nobody talks about enough. The science doesn't just say mould is bad. It says fixing it works.

Get ahead of the moisture, before it becomes mould

A Dew Moisture dehumidifier keeps your home's humidity in the range where mould simply can't thrive. Browse our dehumidifier range — sized for everything from a single bedroom to an open-plan family home.

About the author: Kath P is a writer and researcher covering indoor mould, humidity and environmental health at The Dew. Journal. Her work draws on WHO guidelines, peer-reviewed research and the real-world experiences of Australian homeowners and renters.