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How harmful is damp and mould in UK homes and who is most at risk?

Thousands of people, including babies and toddlers, are hospitalised each year with lung conditions linked to damp and mould-ridden homes. As part of a Guardian series looking at the state of housing, in particular in the private rented sector, here we examine how damp and mould affect the body and mind, who is most at risk and what can be done.

How common is damp?

Across the UK, about 3% of flats and homes are classified as having damp. But this official figure counts only those cases deemed severe enough to sway a surveyor’s house health safety assessment. Far more homes are affected in practice and the impact is not evenly spread. In white British households, prevalence of damp sits at about the national average. In some black and Asian households it is two to three times higher. There are substantial generational and socioeconomic divides, too: damp is five times more common in private rentals than in owner-occupied homes.

What causes damp?

Damp is excess or unwanted moisture, and it builds up in homes through a number of routes. The most common is condensation, visible as water droplets on windows or walls. It forms when moisture in the air, from showers and baths, kettles and pans, and damp clothes hung over radiators, condenses on colder surfaces. There’s also rising damp, where groundwater is drawn up into walls, and penetrating damp, where water enters through the building’s fabric, for example through roof or masonry damage, gaps around doors and windows, or poorly maintained pipes and guttering.

Why is it a problem?

Damp affects mental and physical health. Doctors see more depression and anxiety in people living in cold and damp homes, and the distress can impair immunity, hormone function and the cardiovascular system. The stress can also drive more smoking, eating and alcohol consumption.

Damp also affects building materials and furnishings, driving chemical reactions and deterioration that release potentially harmful chemicals into the air, where they can be breathed in.

A major problem with damp is that it encourages the growth of particular dust mites, bacteria, moulds and viruses, which can cause allergic reactions and disease. Visible, musty-smelling mould can build up on damp window frames and form patches on carpets, walls, floors and ceilings. “Visible mould has to be dealt with,” says Dr Chris Kosmidis, a consultant in infectious diseases at the National Aspergillosis Centre in Manchester.

What is mould?

Mould is a form of fungus that divides into about a million different species. Humans come into routine contact with about 200 of them, though fewer than 50 tend to show up in homes, schools and other indoor spaces. Among the most common are cladosporium, aspergillus, penicillium, alternaria and the toxic black mould stachybotrys, which often grows on building materials that have been damp for a long time, such as after a flood.

How harmful is mould?

Moulds release tiny spores in their thousands that are carried in the air. These microscopic particles can trigger allergic reactions in about 5% of the population. In dry and well-ventilated buildings, spores are rarely a problem. But when mould takes hold, spores can build up.

“The spores will get to densities that are pathological,” says Prof Matthew Fisher, a fungal epidemiologist at Imperial College London who sits on Defra’s air quality expert group.

Mould spores can cause itchy eyes and eczema, but the most common problems are respiratory conditions. “All of us inhale these spores and they end up in the lower airways of the lungs,” says Kosmidis.

The effects can range from a stuffy nose, coughs and wheezes to life-threatening asthma attacks and infections. A study by the US Environmental Protection Agency attributed more than a fifth of national asthma cases to damp and mould.

In some patients, often those with lung damage from tuberculosis, cystic fibrosis or chronic obstructive pulmonary disease (COPD), inhaled mould can become an established infection. In people with severely weakened immune systems, the mould can occasionally spread from the lungs, leading to potentially fatal infections in the brain, heart and kidneys.

Who is most at risk?

Anyone can develop health issues from damp and mould, but those with existing medical conditions are hit hardest, as well as children and older people. People with allergies, asthma, COPD, cystic fibrosis, other lung diseases or cardiovascular disease are at greater risk of their conditions worsening and developing fungal infections.

Common moulds such as cladosporium, alternaria, aspergillus, and penicillium are known to exacerbate asthma, and there is growing evidence that spores can cause childhood asthma in the first place.

A study for the US National Institutes of Health found that the risk of babies developing asthma rose in line with mould levels at home. A 2022 report on air pollution by England’s chief medical officer, Prof Chris Whitty, noted that children who grow up with mould in the home are up to three times more likely to have coughs and wheezes indicative of asthma and other respiratory illnesses.

How do you prevent mould?

Damp is easier and cheaper to deal with the sooner it is acted on. Persistent leaks and water damage are likely to need professional repairs, with affected material ripped out and replaced, but finding the source of the water is a good place to start. A simple fix to a leaky pipe or damaged gutter may be all it needs.

Condensation is a bigger problem in the winter when windows and external walls are colder surfaces for water to form on. Try to reduce the amount of moisture in the air and ensure ventilation.

Simple measures can make a huge difference, such as cooking with pan lids on, not drying clothes on radiators, and putting cold water in the bath before adding hot to reduce the amount of steam produced.


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