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Mould and indoor air quality in your house: What you should know


There is sufficient evidence to suggest a link between dampness and mould in buildings with increased risks of adverse health effects for the occupants. As a silent killer, mould causes unseen problems such as poor indoor air quality, airborne contamination and a host of allergens.

© Getty

Indoor air quality, sick building syndrome, building-related sicknesses and environmental health has been widely associated with dampness in buildings, which is caused by water damage, leakage and wet spots, and is a common problem in many countries. Consequently, mould outbreaks and microbial infections have been a public concern since the 1990s.

The World Health Organization (WHO) has also published the “WHO Guidelines for Indoor Air Quality: Dampness and Mould” in 2009 to tackle the global public health concern of microbial growth due to dampness in buildings. Various researches and scientific publications have found that visible mould is positively associated with asthma, wheeze and allergic rhinitis.

The indoor mould risk in Malaysia

We live in a tropical area with abundant rainfall and sunshine throughout the year. The average rainfall is as high as 2500mm per annum and the average temperature is 27°C.  In general, the ambient humidity is high, ranging from above 60% relative humidity (RH) in the daytime to approximately 100% at night in the outdoor environment.

In comparison to the hot and humid weather outdoors, the relative humidity in the indoor environment ranges within 60% to 70% RH in our buildings.  However, in areas with higher dampness like toilets, kitchens, non-shaded external walls, drain surfaces and laundry areas, the RH is higher. Black, yellowish, green or brown circular mouldy spots can be easily found in these places. In addition, these circular spots can be found on leaky ceilings where they are often regarded as common and negligible stains in Malaysia.

Universiti Malaya microbiologist Prof Dr Vikineswary Sabaratnam has researched mouldy spots with samples collected from external walls throughout Malaysia. She isolated more than 100 types of microorganisms from the samples, including mould, bacteria, viruses, algae, protozoa and microscopic animals, mites and plants. Most of these microorganisms are harmless. Some are health hazard pathogens.

What causes mould to form in the house?

interfloor leakage in high rise
© Paulus Rusyanto/ 123RF

Indoor environments normally contain settled fungal spores, airborne bacteria and other microorganisms, all waiting for hospitable growth conditions. Nutrients are readily available on fibrous and cellulose materials like upholstered and wooden furniture, plywood, chipboards, MDF boards, paint, food waste and shed skin. The normal indoor oxygen level and temperature (29°C to 34°C) are rather conducive for the growth of microorganisms. As a result, moisture level becomes the determining condition in the growth of microorganisms.

Building occupants should not wait for mould to grow, but instead should be vigilant against dampness in their homes. In general, mould starts to grow in a hospitable environment if the dampness lasts for more than 24 hours.

Damp indoor spaces also attract dust mites, termites, insects, cockroaches and rodents. Furthermore, microbial growth induced by indoor dampness has been linked to allergy and infection at the respiratory tracts and skins of people with impaired, deteriorating or under-developed immune systems.

How harmful is mould in homes and buildings?

As most Malaysians spend approximately 90% of their time indoors, an excessive presence of bacteria and mould in buildings poses a health hazard, even in healthy adults. Some species of bacteria and mould can produce spores and/or endoscopes. Some of these microorganisms produce enzymes that cause decay on building materials, adversely affecting the structural integrity and authenticity of the buildings. On top of that, these microorganisms produce unpleasant musty odours.

Healthy adults can resist pathogenic airborne microorganisms with a total bacterium count of up to 500 CFU/m3 and a total fungal count of 1,000 CFU/m3, according to the Industry Code of Practice for Indoor Air Quality 2010 in Malaysia. However, the young, old, sick and pregnant have lower immunity and are more susceptible to the invasion of these airborne pathogens.

What are the health problems caused by mould?

indoor air quality mould house
© 123RF

Many moulds that thrive in damp indoor environments produce mycotoxin and microbial volatile organic compounds (mVOC) which cause a mouldy musty odour. Some of these mycotoxins and mVOCs are carcinogenic and/or toxic. In poorly ventilated indoor environments, the concentration of these toxins in the indoor air increase over time, causing a consequential drop in indoor air quality. Inhalation of these toxins can cause effects ranging from short-term irritation to immunosuppression, severe dermatosis on the skin and cancer.

Inhalation of excessive spores and mould fragments can cause the immune systems to overreact to these allergens and lead to symptoms such as coughing, itchy eyes and other misery. In some people, mould allergy is linked to asthma. Exposure causes restricted breathing and other airway symptoms. According to America’s Centre for Disease Control and Prevention (CDC), children in homes with visible mould are 49% more likely to have asthma than those who are not. In addition, the risk of nasal allergies is 39% higher among children in mouldy houses, too.

Continuous exposure to bacteria and mould spores, fragments and metabolites (mycotoxin and mVOCs) can weaken the immune system and bring allergy, resulting in opportunistic infections.

Symptoms of mold sickness

A study in 2004 by the Institute of Medicine, USA lists down the following ill-effects of damp indoor spaces to health:

1. Upper respiratory tract symptoms including nasal congestion, allergic rhinitis “hay fever”, sneezing, runny or itchy nose, sinusitis and sore throat.

2. Lower respiratory tract symptoms including phlegmy coughs, wheezing, chest tightness and shortness of breath.

3. Hypersensitivity pneumonitis which is a lung disease resulting from exposure and sensitisation to antigens inhaled with a variety of organic dust. Symptoms include dry cough, dyspnea, fever and sometimes acute bronchospasm.

4. Fungus-related illnesses in people whose immune system is severely immunocompromised and who have chronic obstructive pulmonary disease (COPD). Severely immunocompromised persons include those who undergo high-dose cancer chemotherapy and recent recipients of solid-organ transplants.

5. Respiratory infections which can result from exposure to fungi, including Aspergillusspp. and Fusarium spp.

6. Potential lung infection from exposure to fungi such as Aspergillus, in people with some chronic pulmonary disorders including cystic fibrosis and asthma and.


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Is mould contamination severe in Malaysia?

A 2011 study of the link between asthma and fungal DNA, allergens and mycotoxins by Swedish scientists in two secondary schools in Johor found fungi levels to be high enough and mycotoxins detected in up to 22% of classes involved in the study.

The total fungal DNA levels were 50 times higher than a Swedish day-care centre study that used the same sampling method conducted in Sweden. This is attributed to the hot and humid climate conditions in Malaysia which are conducive for microbial growth. It was concluded that fungal DNA and cat allergens were common in Malaysian schools and there was a high prevalence of both doctor-diagnosed asthma and respiratory symptoms among the students.

How to prevent mould infestation in your home?

© 123rf

The recent increase in rainfall, thunderstorms and floods attributed to a global greenhouse effect has made moisture control very challenging in Malaysia.

You should pay attention to mould growth not only on the inside of your house but also outside. A normal 15 to 20 knots wind can carry mould spores on external walls into your house through doors, windows and other openings.

Waterproofing systems

Waterproofing must be installed in areas that get wet regularly (toilets, laundry area, kitchen) as follows: construction of 25mm X 25mm of angle fillets, application of highly elastic and adhesive waterproofing compound, cement rendering and installation of tiles with the desired gradient (1-inch drop per 10 feet). This is to prevent seepage of wastewater from gravity and capillary suction to the adjacent walls.

The plumbing system in your house requires regular maintenance, too. Steel pipes are prone to rust and leak due to exposure to chlorine in domestic water. Other piping and sealing materials like PVC, ABS and PE also have an average life of 15 years.

Rainwater drainage

A slope with a gradient that drains rainwater away from the building (i.e. 5% steepness, 6 inches per 10 ft) is vital to prevent capillary suction (transport of liquids in porous solids) of rainwater through the foundation and the floor. If the steepness of the earth cannot be altered for proper drainage due to unforeseeable limitations, the installation of an underground subsoil system can help prevent groundwater from penetrating into the building.

Building materials to avoid or reduce

© banepx / rf123

Hygroscopic materials and softwood used in buildings also are prone to microbial growth. These include fabrics, plywood, chipboards, MDF boards, timber floor, carpet, lumber for roofs and furniture. The moisture content in these materials is above 10%. Even at a lower level of dampness at say 65% RH, the air adjacent to these surfaces will reach dew points at night (when the temperature is lower), making them hospitable to microbial growth.

Vapour diffusion

Our hot and humid climate causes vapour diffusion into buildings due to a higher vapour pressure in the outdoor environment. Therefore, vapour diffusion retardant is important to prevent such a high inward flow of moisture. In areas with low latitude, sealers and coating systems on the external walls are commonly used due to the ease of application and low costs.

Vapour is also produced when we breathe and during daily activities like showering, washing, combustion, cloth drying and cooking. Ornament water features, aquariums, plants and pets also contribute to indoor humidity. The vapour produced should be vented out using exhaust fans, cooking hoods, vented roof systems and ventilators.

Condensation management

Condensation of water vapour causes wetting of surfaces, promoting microbial growth.

Due to the hot climate in Malaysia, the use of air conditioners is common. In residential buildings, split unit air-conditioners are most common. Prolonged use of air conditioners causes cooling of walls that can extend to the external surfaces of your home. Condensation occurs on the external wall when the cold wall surfaces encounter humid external air.

The copper tubes for the coolant that connect the indoor blower and the external condenser must be sufficiently insulated. Leaking due to condensation can happen with insufficient insulation and wrapping at the joints of the insulation tubes. The best way is to apply double insulation without tightening at the joint of the insulation tubes.

READ: How to remove mold and mildew once and for all

Myths about indoor air quality and biological and mould control

There are a few common myths related to air quality control and clean-up of biological contamination in Malaysia, but these are quick fixes that do not address the underlying problem of moisture intrusion that lead to microbial growth. In many instances, when the symptoms of contamination are covered up this way, they lead to other adverse side effects.

Ozone cleaners

Ozone comprises three oxygen atoms with unstable molecular bonds and is a strong oxidation agent. Some vendors claim that ozone generators which are sold as air cleaners can clean the air via oxidation of organic pollutants, including biological contaminants like bacteria and moulds. They also claim that these ozone generators are safe for indoor use. However, such a claim has been refuted by medical professionals.

The concentration of ozone gas is safe at 0.05ppm. The problem is at 0.05ppm, it has been scientifically proven that it takes too long for the reaction of oxidation to occur, making the cleaning claims dubious. Second, for many of the chemicals with which ozone does readily react, the reaction can form a variety of harmful or irritating by-products.


Ionisers, or electronic air cleaners, are devices that disperse negatively (and/or positively) charged ions into the air. These ions attach to particles in the air, giving them a negative (or positive) charge so that the particles may attach to nearby surfaces such as walls or furniture, or to one another and settle out of the air. In recent experiments, ionisers were found to be less effective in removing particles of dust, tobacco smoke, pollen or fungal spores than either high-efficiency particle filters or electrostatic precipitators.

 Air filters

air filter-indoor air quality

Air filtration systems installed in residential and commercial buildings are designed to trap particulate dust. However, the filtration of large particulate dust can be ineffective for large clouds of dust which will settle from the air quicker on the ground before they reach the filters. High-Efficiency Particulate Air (HEPA) filters and strong blowing fans are more effective.

Nevertheless, air filtration cannot remove contaminating gases like mycotoxin and mVOCs produced by moulds and bacteria.

Perfume sprays

Perfume sprays are widely installed in offices to give some pleasant scent and combat musty odours. However, they cause more harm than good. Researchers have concluded perfume-scented strips exacerbate symptoms and airway obstruction in asthmatic patients. Acetophenone, ethyl acetate and acetone which are present in many perfumes are known as potential respiratory allergens.

Bacteria and mould disinfectants

Bacteria and mould disinfectants can kill and remove microorganisms. However, dead mould fragments and spores are equally allergenic. Furthermore, biocides and antimicrobials can be harmful to humans, pets and wildlife if not used properly. These chemicals should only be used to treat microorganisms on surfaces and structures and in manners prescribed by government agencies.

Anti-microbial coatings

Anti-microbial coatings which integrate nanosilver and other innovative disinfectant chemicals can hardly be applied to the concealed areas where microorganisms grow – these include internal parts of gypsum board partitions and insulation, air ducts and wooden roof trusses. These coatings should not be used for the purpose of moisture control.

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Based on the limited scientific publications available here, bacteria and moulds are common in Malaysia. Amid air quality control gimmicks by vendors, we must adopt a systematic approach to prevent indoor microbial contamination by ensuring dryness, cleanliness and hygiene for our buildings and the occupants. Preventing dampness is key to maintaining indoor air quality and environmental health in the long run.

Proper design, construction quality control and routine maintenance are also necessary for moisture control and prevention of microbial contamination. Currently, statutory requirements relating to microbial growth and exposure limit in Malaysia are available for commercial and industrial buildings only. We can refer to Singapore’s Building Construction Association (BCA), which outlines many good industry practices in construction, including waterproofing of external perimeter walls and planters, dampproof course, proper bricklaying and plastering, material handling and application of sealant. Although these recommendations are not compulsory in Malaysia, they are good measures that we should consider.

Disclaimer: The information is provided for general information only. Malaysia Sdn Bhd makes no representations or warranties in relation to the information, including but not limited to any representation or warranty as to the fitness for any particular purpose of the information to the fullest extent permitted by law. While every effort has been made to ensure that the information provided in this article is accurate, reliable, and complete as of the time of writing, the information provided in this article should not be relied upon to make any financial, investment, real estate or legal decisions. Additionally, the information should not substitute advice from a trained professional who can take into account your personal facts and circumstances, and we accept no liability if you use the information to form decisions.

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