Mould in the home can make you ill

What is mould?

Mould spores are present everywhere. Mould grows in colonies and releases mycotoxins, which help protect it from competitors. These mycotoxins can be found in floor dust, on wood and cellulose-based materials, and on damp plasterboard.

Mould spreads by releasing millions of spores into the air, which means spores are found in all buildings. When the right conditions for growth are present, the spores settle on damp surfaces, begin to germinate, and form new mycelium. Small fragments of mycelium can also become airborne, allowing new colonies to establish.

The size of most mould spores ranges from approximately 2–10 µm (0.002–0.010 mm), meaning they are easily carried by air currents and can enter the human respiratory system.

Mould primarily grows on damp organic materials such as wallpaper, wood, and plasterboard. Mould growth in buildings only occurs when materials are sufficiently damp, with a moisture content equivalent to equilibrium with air at a relative humidity of 75-80%. In other words, when the relative humidity is below 70%, mould is unlikely to develop. However, localised damp conditions, such as moisture penetration in walls, can still occur.

Mould plays an important role in nature’s nutrient cycles and is also used in the food and pharmaceutical industries. However, mould can also cause discomfort and adverse health effects in both indoor and outdoor environments.

How does mould affect human health?

Mould produces allergens (substances that can cause allergic reactions) and irritants. Inhaling or touching mould or mould spores can trigger allergic reactions in sensitive individuals.

Allergic reactions to mould are common and can be immediate or delayed. Mould can also trigger attacks in asthmatics who are allergic to mould.

Irritation

Irritation is the most frequent health effect associated with exposure to moisture and mould growth. Symptoms may include irritation of the eyes, nose, and upper respiratory tract, headaches, fatigue, coughing, and skin rashes. People with hay fever and asthma are particularly sensitive. Additionally, airway irritation can increase the risk of respiratory infections.

Children who grow up in homes with high humidity have an increased risk of developing asthma. In extreme cases, where there is extensive mould growth and a high concentration of mycotoxins in the air, severe toxic reactions have been observed.

Allergy

Allergic reactions can occur with repeated exposure to moulds containing antigenic proteins (allergens). It is rare for individuals to develop mould allergies solely from being in damp buildings, but the risk is higher for those already predisposed to allergies such as hay fever or asthma, or those with sensitive airways. People with an existing allergy to moulds may experience worsening symptoms.

Research into the link between mould and health effects is ongoing.

The importance of regulating the indoor climate

A damp indoor environment can promote the growth of mould and dust mites. As people in the Western world spend 80-90% of their time indoors, a good indoor climate is essential for health and well-being, particularly in relation to moisture, mould, and health.

Moisture damage and mould problems often occur in older buildings with poor insulation and inadequate ventilation.

Relative humidity (RH) refers to the existing water vapour pressure in the air, expressed as a percentage of the saturated vapour pressure at the same temperature. RH reflects both the amount of water vapour in the air and the air temperature. For example, RH will increase if the temperature of an air mass decreases but no water is removed. If the air cools sufficiently, some of the water vapour will condense into liquid water. The highest temperature at which condensation occurs is known as the "dew point."

What are the signs of mould in a building?

If you suspect that health symptoms, such as those mentioned above, are caused by a damp building with mould growth, you should have professionals assess the property.

A prolonged damp issue lasting several weeks or more will typically result in mould growth and the release of spores into the indoor air, increasing the risk of exposure. Short-term moisture problems that dry out within a few days are unlikely to result in mould growth.

Look out for black spots

Mould often appears as black spots but can be difficult to detect because it may grow behind wallpaper or within wall cavities. Mould can also develop in poorly insulated ventilation systems or air conditioning units with clogged drains.

Furniture placed against external walls with limited insulation, as well as walls around bathrooms, are common areas for mould growth. Air from crawl spaces often enters the building and can contain mould spores, fragments, and a musty smell.

Musty odour?

A strong musty smell is a good indicator of moisture problems. This odour is caused by moulds emitting volatile organic compounds (VOCs), which can create a musty or damp smell. However, VOCs in the concentrations found in indoor environments are not considered to directly cause illness. Certain bacteria, particularly those of the Streptomyces genus, which are also associated with damp buildings, can produce strong musty odours.

Why does moisture occur in homes?

There are many reasons for moisture problems in homes:

1. Rising damp. Water from the ground seeps into the building. This is common in older buildings and can also be caused by construction defects in newer buildings. Contributing factors include blocked drains, inadequate sealing of foundations, and insufficient or clogged roof drainage.
2. High indoor humidity due to activities such as bathing, cooking, cleaning, laundry, and human and animal respiration. If more moisture is added to the indoor air than is removed through ventilation, humidity can condense on surfaces, such as windows.
3. Insufficient ventilation, either natural or mechanical.
4. Poor insulation, creating thermal bridges.
5. Water ingress from flooding or rain.
6. Water damage in building structures due to inadequate drying of building materials or construction defects, which can also occur in newly built properties.
7. Pipe leaks, either visible or hidden, caused by corrosion, ruptures, or leaking joints. Apart from major floods, small undetected leaks are the most damaging, as they can create moisture problems over time, fostering mould growth and damaging materials and building structures.

How can you prevent mould in your home?

To minimise health risks, it is crucial to identify and address the cause of dampness quickly, remove mould growth effectively, and ensure rapid drying of affected areas to prevent recurrence. In some cases, you may be able to do this yourself, but professional assistance is often required to ensure the work is done properly. Any water damage must be repaired, as it not only causes mould growth but can also weaken the building’s structure and insulation properties.

Building professionals can conduct a technical inspection of a property, focusing on mould growth. Samples may be taken from walls, wallpaper, woodwork, and other materials to identify mould growth in moisture-damaged areas.

Lower humidity levels

Reducing humidity is essential, either by increasing ventilation or through dehumidification. Heating alone is not a sufficient solution. Warm air can hold more moisture than cold air, leading to lower relative humidity. However, when warm air comes into contact with cold surfaces, humidity can condense as moisture. This is often seen around windows, in poorly insulated areas (thermal bridges), or in inadequately heated rooms. Keeping bedroom temperatures low can encourage mould growth in these spaces, so bedrooms should be well-ventilated and heated during the day.

If a damp wall remains warm due to sunlight or proximity to a boiler room, mould growth can develop rapidly, as higher temperatures promote growth.

Ideally, indoor humidity should be kept below 70% and preferably maintained at 45-50%. This can be achieved through stable temperatures, ventilation, and, if necessary, dehumidification.

Various moisture meters can measure both relative humidity and material moisture levels.

For more information on how Dantherm Group can assist professionals with handling mould projects, please contact us today.

Sources:

• Mold and Health. United States Environmental Protection Agency (https://www.epa.gov/mold/mold-and-health).
• Damp Indoor Spaces and Health. Institute of Medicine Committee on Damp Indoor Spaces and Health. Washington (DC): National Academies Press (US), 2004. (https://www.ncbi.nlm.nih.gov/books/NBK215649/).
• "Health Issues Related to Damp and Mould in Buildings – On Assessment and Diagnosis in General Practice" (Original title: Helbredsproblemer ved fugt og skimmelsvampe i bygninger – Om udredning og diagnostik hos alment praktiserende læger). Danish Health Authority 2006 (https://www.sst.dk/da/udgivelser/2006/Helbredsproblemer-ved-fugt-og-skimmelsvampe-i-bygninger---om-udredning-og-diagnostik-hos-alment-prak)
• www.skimmel.dk – An independent danish knowledge centre operated by the National Building Fund, the Landowners' Investment Fund, and BUILD (formerly the Danish Building Research Institute).