GAtherton

Summary: A recent rapid review by researchers from the Health and Safety Executive examined evidence on microbiological hazards in buildings, including moulds, bacteria and viruses. The review highlights that dampness, poor ventilation and building design can all affect indoor air quality and respiratory health.

Key points

• People spend much of their time indoors, so indoor air quality can strongly affect health.
• Damp indoor conditions increase the risk of mould growth and musty odours.
• Common indoor moulds include Aspergillus, Penicillium and Cladosporium.
• Dampness and visible or hidden mould are linked with asthma, rhinitis, wheeze and other respiratory symptoms.
• Ventilation is one of the most important ways to reduce moisture and dilute airborne contaminants.
• Improving energy efficiency is important, but very airtight homes still need adequate ventilation.

Contents

• Why indoor air matters
• What the review found
• Damp, mould and lung health
• Aspergillus and aspergillosis
• Ventilation and building design
• What can help reduce risk?
• Help us understand damp homes and health
• When to seek medical advice

Why indoor air matters

Most of us spend a large amount of time indoors — at home, at work, or in public buildings. The air inside buildings can contain particles from many sources, including dust, mould spores, bacteria, viruses, cooking, cleaning products, pets and outdoor air entering the home.

The recent review, Exposure Risks from Microbiological Hazards in Buildings and Their Control — A Rapid Review of the Evidence, looked at evidence for harmful microorganisms in indoor air and on surfaces, and how building design, ventilation and moisture affect exposure.

What the review found

The review found strong evidence that microorganisms can be present in indoor air and on surfaces. These include fungi, bacteria and viruses. The evidence was strongest for the role of dampness and poor ventilation in increasing the risk of indoor mould growth and respiratory health effects.

The review’s main conclusions included:

• Airborne allergenic fungi are well documented in indoor air.
• Damp conditions increase mould growth and mouldy odours indoors.
• Dampness and mould are associated with respiratory ill health, including asthma, rhinitis and wheezing.
• Penicillium, Aspergillus and Cladosporium are commonly detected in damp buildings.
• Infectious viruses and bacteria can also be detected in indoor air and on surfaces.
• Ventilation is a key control measure for reducing moisture and diluting airborne contaminants.

Damp, mould and lung health

Dampness is one of the most important drivers of indoor mould growth. Moisture can come from leaks, condensation, flooding, poor insulation, inadequate heating, drying clothes indoors, cooking, showering, or poor ventilation.

When dampness persists, mould can colonise indoor materials such as plasterboard, wallpaper, wood, carpets, soft furnishings and settled dust. Mould may be visible, but it can also grow in hidden areas such as behind furniture, inside wall cavities, behind wallpaper, under flooring, or around poorly ventilated cold surfaces.

Exposure to damp and mould has been linked with:

• Wheezing
• Asthma symptoms or asthma worsening
• Rhinitis and nasal symptoms
• Cough
• Respiratory infections
• Worsening symptoms in people with existing lung disease

Importantly, the review notes that the relationship between indoor microorganisms and health is complex. Risk depends on the type of organism, the level of exposure, the building conditions and the susceptibility of the person exposed.

Aspergillus and aspergillosis

Aspergillus is a common mould found in the environment. Most people inhale Aspergillus spores every day without becoming ill. However, some people are more vulnerable, including those with asthma, bronchiectasis, chronic lung disease, weakened immune systems, or previous lung damage.

In susceptible people, exposure to Aspergillus may contribute to conditions such as allergic bronchopulmonary aspergillosis (ABPA), severe asthma with fungal sensitisation (SAFS), aspergillus bronchitis, or chronic pulmonary aspergillosis (CPA). The home environment is not the only source of exposure, but damp indoor spaces may increase the amount of fungal material a person breathes in.

This does not mean that every damp home causes aspergillosis, or that every person exposed to mould will become ill. It does mean that reducing dampness, improving ventilation and addressing visible or hidden mould are sensible steps for respiratory health.

Ventilation and building design

One of the strongest messages from the review is that ventilation is central to controlling indoor microbiological risk. Ventilation helps by:

• Removing moisture from indoor air
• Reducing condensation
• Diluting airborne mould spores and other particles
• Reducing the build-up of infectious aerosols
• Improving overall indoor air quality

The review also highlights an important modern problem. Homes are increasingly designed or retrofitted to be more airtight and energy efficient. This can improve warmth and reduce energy use, but if ventilation is inadequate, moisture and airborne contaminants may accumulate indoors.

In other words, insulation and energy efficiency are important, but they need to be balanced with effective ventilation and moisture control.

What can help reduce risk?

The review does not suggest that one single action solves all indoor air problems. Instead, it supports a combined approach.

1. Reduce moisture

• Repair leaks promptly.
• Check roofs, gutters, pipes and window seals.
• Use extractor fans in kitchens and bathrooms where available.
• Avoid drying clothes indoors where possible, or ventilate well if you do.
• Reduce condensation on windows and cold walls.

2. Improve ventilation

• Use trickle vents if fitted.
• Open windows when safe and practical.
• Use mechanical ventilation systems correctly.
• Keep air bricks and vents clear.
• Make sure extractor fans are working effectively.

3. Deal with mould safely

• Small areas of surface mould may be cleaned carefully using appropriate household methods.
• Large, persistent or recurring mould usually needs the underlying damp problem fixed.
• People with significant lung disease, immune suppression or severe symptoms should avoid heavy mould disturbance and seek advice.

4. Reduce dust reservoirs

• Regular cleaning can reduce settled dust and spores.
• HEPA-filter vacuum cleaners may be helpful for some households.
• Hard flooring may be easier to keep dust-free than carpets in high-risk situations.

5. Consider air filtration where appropriate

Portable high-efficiency particulate air (HEPA) filters may help reduce airborne particles in some settings. They are not a substitute for fixing damp or improving ventilation, but they may be a useful additional measure for some people.

Help us understand damp homes and health

The evidence linking damp homes, mould and respiratory health is strong, but there are still important unanswered questions. We need to better understand how different homes, building types, ventilation patterns and damp conditions affect people’s health in real life.

The National Aspergillosis Centre is running a UK citizen science study looking at damp homes and health.

We are inviting people to register their interest in taking part.

The study is open to people with and without lung conditions, and to people living in homes with or without damp or mould. This comparison is important because it helps researchers understand which factors are most strongly linked with health outcomes.

Register your interest in the damp homes and health study

Taking part may involve completing a questionnaire and, at a later stage, providing a dust sample from your home. The information gathered will help improve understanding of indoor environments and respiratory health.

When to seek medical advice

Please seek medical advice if you have:

• New or worsening breathlessness
• Chest pain
• Coughing up blood
• Persistent fever
• Repeated chest infections
• Rapidly worsening asthma symptoms
• Unexplained weight loss or severe fatigue

If you already have aspergillosis, asthma, bronchiectasis, chronic obstructive pulmonary disease (COPD), immune suppression, or another lung condition, it is worth discussing any significant damp or mould exposure with your healthcare team.

Common questions

Can mould affect health even if I cannot see it?

Yes. Hidden mould or dampness may still affect indoor air quality. A musty smell, persistent condensation or symptoms that worsen in a particular room may suggest a problem.

Does all mould cause aspergillosis?

No. Mould exposure is common, and most people do not develop aspergillosis. Aspergillosis usually occurs when exposure combines with individual susceptibility, such as asthma, bronchiectasis, immune suppression or existing lung damage.

Is ventilation always good?

Ventilation is usually important for reducing moisture and improving indoor air quality. However, the best approach depends on the building, outdoor conditions and the person’s health. Ventilation should not replace fixing leaks or removing sources of damp.

Can air purifiers solve damp and mould problems?

No. Air purifiers may reduce airborne particles, but they do not remove the source of moisture or mould growth. Damp problems need to be addressed at source.

Summary

This recent evidence review reinforces a practical message: indoor air quality matters. Dampness, poor ventilation and mould growth are not simply cosmetic housing problems — they can affect respiratory health, especially in people with asthma, aspergillosis or other lung conditions.

The most effective approach is to reduce moisture, improve ventilation, remove mould sources where possible and understand how buildings influence exposure. Research such as the UK damp homes and health study will help build better evidence for patients, clinicians, housing providers and policymakers.

References and further reading

• Beswick A, Crook B, Gosling B, et al. Exposure Risks from Microbiological Hazards in Buildings and Their Control — A Rapid Review of the Evidence. Atmosphere. 2025;16:1243. doi:10.3390/atmos16111243.
• Damp homes and health study — register your interest
• Aspergillosis.org — patient and carer information