Mould: What does it mean for indoor air quality?

~ Dr. Christina Vlahopoulos, ND, MSc (cand.)

With spring just around the corner it means we will start opening windows to let the fresh air in. It is also a very damp time of year with a lot of rain – for those who suffer from mould allergies, it can be challenging. There is a lot of strong evidence suggesting that dampness outside can change indoor air quality. But how does moisture make us sick? Unfortunately it is not the water and rain that make us sick, but rather they create the perfect environment and conditions for mould to grow.

Mould spores can be found everywhere – from food to drywall to leaf litter and the soil on the ground. In fact, mould and the enzymes they secrete, are needed for the normal breakdown and decay of organic material. But the problem begins when there are higher concentrations of mould indoors than outdoors. The problem gets worse when the perfect conditions are met for it to grow. All mould needs is increased moisture or water accumulation and/or the indoor relative humidity level to be above 60% – the higher the moisture content, the faster the mould growth. The greater the mould growth, the higher the risk for poor indoor air quality and the greater the chance of breathing problems or other respiratory illnesses.

One type of mould called “black toxic mould” should not normally be in an indoor environment and when it shows up, it means there are serious water problems in the home. It can create poor indoor air quality and cause people to have symptoms such as: chronic sinusitis, coughing, wheezing, asthma, congestion, a hoarse voice and some people even report feeling foggy headed. Many moulds are black in colour but not all black moulds are toxic, therefore if you find mould in your home it is important to have it assessed by professionals and if found to be toxic, to have the professionals remove it properly. It is also important to not only clean the mould, but to find where the moisture is coming from and deal with the cause.

The best way to increase indoor air quality is prevention: reduce moisture content by keeping relative humidity below 50% with a dehumidifier, use an air exchanger and/or air purifier and ventilate your house appropriately. Finally, after a good nights’ rest, mattresses and bedding maintain high levels of moisture so it is important to let your bed air out by folding down your blankets to expose your sheets. Now you finally have that excuse to NOT make your bed in the morning!

Molot, J. (2012). Biological Indoor Air Pollutants, Adverse Health Effects, Prevention [PowerPoint slides]. Lakehead University, Thunderbay Ontario.

environment, stress


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We respectfully acknowledge that Kingston Integrated Healthcare is situated on ancestral Anishinaabe and Haudenosaunee Territory. Since time immemorial they have cared for these lands and waters, and we are grateful. We recognize that a healthy environment is essential to the wellbeing of all people and all life.

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