Damp homes and human health

22 September 2021

By Graham Atherton, National Aspergillosis Centre, Manchester University NHS Foundation Trust

Damp homes have several causes. These can be obvious to the householder – eg. leaking water pipes, dripping guttering, broken roofing and, increasingly commonly as global warming exerts its influence on our weather, flooding (1). These are usually easy to spot, even for the nonprofessional, and a repair is straightforward.

Less obvious might be hidden leaks, such as broken sewage pipes and defective damp courses, that consequently are often left to the professional surveyor to detect.

Perhaps least obvious of all is the damp that has no obvious source. Sometimes its impact is noticeable as condensation on the inside of windows or on cold pipes. What many do not appreciate is that this moisture can also settle on interior walls, settling into plasterwork and even on soft furnishings at night when the room temperature drops. It often soon dries when the heat rises again, but the damage is already done. Microbes can start to germinate and grow under such conditions, particularly if this is a repeated nightly cycle.

Where does this moisture come from?

It comes from you, me, and our normal activities of daily living. We exhale moisture with every breath, we shower amid clouds of steam and cook and launder with copious amounts of hot water. Breathe onto a cold window and watch your breath condense onto the glass with every exhale. All that moisture is hidden in the air and will stay there until it cools down. The warmer the air is, the more moisture it can hold, ready to be released when it cools.

100 years ago, when our homes were draughty and heated by open fires, all the moisture suspended in the air in our homes would quickly have been sucked up a chimney and away. However, 50 years ago in the UK we decided, with very good intentions, to start to save energy by making our homes less draughty and to stop using open fireplaces. All that moisture in the air is now trapped indoors – and when that happens the building can become excessively damp.

Why is damp in our homes a problem?

As any occupier of a damp home will tell you, there can be pools of water under windows, water stains on walls and – one of the most obvious signs of excess moisture – mould growing on walls, ceilings and furniture. What you cannot easily see is the increase in the presence of other microbes that also love to grow in those warm damp places (2). These microbes can be rich sources of allergens, toxins and volatile compounds, all of which can irritate the airways of sensitive people.

The indoor spaces of our homes are incredibly complex places and we have discovered hundreds (thousands?) of different species of microbes living on the surfaces of the building and on (and in!) its occupants. Sources of airborne irritants that might affect our airways can also come from cooking, aerosols, open fires, cleaning materials and more.

What are the health outcomes of all those pathogens/allergens/irritants?

The medical profession has long struggled with the relationship between damp and health. It is very difficult to accurately decide which people are likely to be sensitive to a damp home, and there is very little good information on what might be a dose-response relationship between levels of pollution/damp and consequent health symptoms.

Researchers have made good progress predominantly on respiratory symptoms resulting from exposure to damp indoor air. Illnesses such as asthma (4) and other infections (5) have been well studied, as have allergies (6) and eczema (several other candidates for health outcomes have been proposed but as yet lack the weight of evidence needed to support their mention here).

In 2016, the Royal College of Physicians and Royal College of Paediatrics and Child Health, led by Sir Stephen Holgate CBE, published a report on the impact of air pollution on human health. That report (7) included pollution of indoor air. It strongly supports the evidence mentioned above about which health conditions may be caused by exposure to damp homes, and it goes into the problem much more deeply by looking at a long list of potential respiratory irritants that are present in our homes but are not necessarily associated with damp. This report attempts to bring us a more complete picture of indoor air pollution, and the broader range of illness that can result from it – from stroke, cancer and cardiac health problems to the less well understood symptoms of fatigue, mental illness and headache.

What can we do about this health problem?

A constant supposition is that the indoor space is enclosed and thus the concentration of the many harmful substances can build up to a level that can have an impact on human health. These substances may act individually (eg. moulds, house dust mite, pollen, endotoxins) or in combination in ways we do not yet understand.

Clearly, we need to understand what the sources of these indoor pollutants are, and we need to reduce their emission as much as possible. Unfortunately, that is a difficult task and we have already spent decades learning which pollutants may relate to which health outcome in a ‘sick building’ without coming to many clear and helpful conclusions.

Perhaps it is better to focus on what we know we can change and what an effective intervention might be without being too concerned about sources of these pollutants? We know that excess damp is harmful to respiratory health and we know that many irritants are airborne. Consequently, we should, as a minimum, ensure that our homes are dry and the air that we breathe indoors is regularly exchanged with less polluted outside air. For many of us, both can be achieved by increasing the rate of air exchange using ventilation.

The National Institute for Health and Care Excellence (NICE) recently produced detailed guidance intended to raise public awareness of the importance of good air quality in our homes (8). It is hoped that a range of authorities will use these guidelines to help improve indoor air quality nationwide.

The report is split into several sections, but in the section intended for the general public, improving ventilation and making people aware of the sources of damp and other pollutants play a prominent role. Awareness, education and advice on how to carry out interventions to prevent poor indoor air quality are clearly part of the solution. In certain contexts, these guidelines will be enough to improve indoor air, though they are limited when the context changes – for example:

  • As the weather gets colder outside how do we ensure we can both maintain a safe, comfortable temperature inside the home while at the same time ensure there is adequate air exchange to keep the levels of damp air and indoor pollutants down?
  • How do we ensure that increased ventilation in some homes is not bringing in harmful levels of outdoor air pollution eg. in inner cities where heavy traffic produces harmful levels of irritant gasses and particulates?

As global weather changes and becomes more intense these problems are likely to worsen with more flooding and more extreme climate temperatures. There is a pressing need to ventilate our homes more effectively and at the same time reduce heat loss as we strive to reduce our carbon footprint.

At least the heavily polluting internal combustion engine is currently being consigned to history, which should help reduce levels of several important airborne pollutants that find their way into our homes. But there is a long way to go to ensure that we are all safe from harm in the very place many of us feel safest: our homes.



  1. https://pubmed.ncbi.nlm.nih.gov/29415354/
  2. https://microbiomejournal.biomedcentral.com/articles/10.1186/s40168-017-0356-5
  3. https://pubmed.ncbi.nlm.nih.gov/29683210/Moisture & asthma in the UK
  4. Indoor environmental exposures and exacerbation of asthma: an update to the 2000 review by the Institute of Medicine – PubMed (nih.gov)
  5. Association of residential dampness and mold with respiratory tract infections and bronchitis: a meta-analysis – PubMed (nih.gov)
  6. Respiratory and allergic health effects of dampness, mold, and dampness-related agents: a review of the epidemiologic evidence – PubMed (nih.gov)
  7. Every breath we take: the lifelong impact of air pollution., Royal College of Physicians (RCP) And Royal College of Paediatrics and Child Health (RCPCH 2016)

Indoor air quality at home https://www.nice.org.uk/guidance/ng149


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