Improving Indoor Air Quality by Understanding Moulds and Fungi

Have you ever wondered why mould tends to grow inside homes and buildings? Moulds and fungi are natural components of our environment, essential for breaking down leaves, wood, and other plant debris. These micro-organisms can find their way into a building either directly or through airborne spores. In indoor spaces, you’ll typically discover moulds and fungi thriving on materials such as wood, plaster or drywall, upholstery, fabric, wall paper, drapery, ceiling tiles, and carpeting.

The pivotal factor that fuels the growth of moulds and fungi is moisture. Without it, they simply cannot flourish. Consequently, you’ll often find these unwelcome guests in areas of your home or building that are prone to dampness, such as basements, kitchens, and bathrooms.

In contemporary buildings, moisture issues can arise from various sources, including flooding, roof or plumbing leaks, insufficient ventilation, and everyday activities like cooking and bathing. Excessive humidity can also provide a conducive environment for mould growth. In this article, we’ll use the term “mould” to encompass all types of mould (or mold), mildew, yeasts, and fungi.

Understanding the Types of Mould

While it’s fascinating to identify the specific type of mould growing in your space, it’s not essential for addressing health risks and removal. According to the Centers for Disease Control and Prevention (CDC), all moulds should be treated equally in terms of health concerns and remediation. Some of the more common mould types found in buildings include Stachybotrys chartarum (black mould), Aspergillus sp., Penicillium sp., Fusarium sp., Trichoderma sp., Memnoniella sp., Cladosporum sp., and Alternaria sp.

The Health Impact of Mould

The presence of mould doesn’t guarantee that health problems will occur, but for some individuals, inhaling mould, its fragments, or spores can lead to health issues or worsen existing conditions. Many moulds produce mycotoxins, which are toxic compounds harmful to humans. These mycotoxins can trigger allergic reactions or respiratory problems.

Common symptoms associated with mould exposure include eye, nose, and throat irritation, cough or congestion, aggravated asthma, fatigue, headaches, and difficulty concentrating. Mould can also exacerbate allergy symptoms, such as wheezing, chest tightness, shortness of breath, nasal congestion, and eye irritation. People with weakened immune systems or those recovering from surgery are particularly susceptible to health problems caused by mould.

Preventing Mould Contamination

Moulds have a knack for growing almost anywhere, provided there’s moisture. Therefore, the most effective preventive measure is to reduce moisture levels.

Start by identifying and addressing the source of moisture. To maintain optimal indoor humidity levels between 30% and 50%, consider the following precautions:

  1. Ventilate moisture-generating sources like showers and cooktops directly outside.
  2. Use air conditioners and dehumidifiers to control humidity.
  3. Employ exhaust fans when cooking, washing dishes, or doing laundry.
  4. Insulate cold surfaces to prevent condensation.
  5. Maintain your building and HVAC systems in good condition.
  6. Promptly clean up any floods or spills.
  7. Remove stains from floors and carpets promptly.
  8. Avoid installing carpets near sources of water or on moisture-prone surfaces like concrete.
  9. Remember to maintain your air conditioners and dehumidifiers to prevent them from contributing to moisture issues.
  10. If you use humidifiers, ensure they are cleaned regularly.
Inspecting for Mould

A visual inspection remains the most reliable method for detecting mould problems. Look for signs of water damage, such as discolouration and staining, which are common indicators of mould presence.

Mould typically appears as dark spots, stains, or patches. During the inspection, thoroughly examine areas like ceiling tiles, walls, flooring, window sills, insulation, furniture, and HVAC components.

Keep an eye out for standing water as well, as it can exacerbate moisture issues and mould growth.

Health Canada advises against testing the air for mould, emphasizing that it doesn’t provide information on health risks or the root cause of mould damage. You don’t need to identify the specific mould type to address the issue.

However, you can use moisture monitoring devices to gauge whether moisture levels are conducive to mould growth.

Cleaning Up Mould

Once mould is detected, it’s crucial to identify the source of moisture and rectify it. Generally, it’s recommended to replace porous materials like plaster board, ceiling tiles, fabric, books, and cardboard rather than attempting to clean them. Non-porous materials like metal, glass, hard plastic, and semi-porous materials like wood and concrete can be cleaned and reused if structurally sound.

Cleaning should be conducted using soap or detergent, when less than the size of a standard door, 1 m square. Dust generation should be minimised. When vacuuming, use a High-Efficiency Particulate Air (HEPA) filter. The cleaning approach depends on the extent of the mould damage:

  1. Small Isolated Areas (1-3 patches of mould, each less than 1 square meter/10 square feet):
    • Use respiratory protection, rubber gloves, and eye protection.
    • Remove materials that can’t be cleaned and seal/cover the rest.
    • Clean with a dilute soap or detergent solution, avoiding over-wetting drywall.
  2. Medium-Sized Areas (more than 3 patches or between 1-3 square meters/10-32 square feet):
    • Use a disposable N-95 respirator, gloves, and eye protection.
    • Seal the work area, shut down HVAC if needed, and employ dust suppression methods.
    • Clean with water and soap or detergent, ensuring the area is dry and free of contamination when finished.
  3. Larger or Highly Contaminated Areas (greater than 3 square meters/32 square feet):
    • Leave such projects to trained professionals.
    • Workers should wear disposable protective clothing, use a full-face HEPA respirator, and isolate the area.
    • Create negative pressure with an exhaust fan and HEPA filter.
    • Clean and dispose of materials properly.

When mould is present in the HVAC system, professional assistance is advisable. Small-scale contamination can be cleaned using similar methods as for small surface areas, while large-scale contamination should be handled by professionals. Remember not to use chemical disinfectants like bleach for mould remediation, as they can pose health risks and avoid vacuuming without HEPA filtration.

Seal mouldy materials in plastic bags for disposal, and clean the work area thoroughly.


Understanding mould and fungi growth, their potential health impact, and effective prevention and remediation techniques are essential for maintaining indoor air quality. By addressing moisture issues promptly, conducting regular visual inspections, and following proper cleaning guidelines, you can significantly reduce the risks associated with mould and ensure a healthier living environment for you and your loved ones.

  1. EPI Mold Guidelines Health Canada
  2. Centers for Disease Control and Prevention (CDC) – Mold
  3. National Institute of Environmental Health Sciences – Mold
  4. Environmental Protection Agency (EPA) – Mold


  • Carol Parr

    We’re glad you’re here. We’re Carol and Tony, founders of one of the longest running Healthy Home Blogs in the world, Mitey Fresh Australia. We’ve been on this journey for the last 25 years and are passionate about helping families sift through health hazards and triggers like allergens, mould, water damage, chemicals and EMFs, to get clarity about what’s toxic and what’s not so they can create a healthy and happy home for their family they love. Each month, people visit this blog seeking focus on the health and wellbeing of their loved ones, sustainable and effective practice tips and guides, to help create and manage healthier indoor spaces, improve the built environment that is pleasing to the senses and support healthy living and nature, every day. Starting this blog was to help change people’s lives, one family at a time, and we can’t wait to share how its allowed us to stand next to you and show you how interpreting these synergies between buildings and the environment they are built in will impact upon the health and well-being of those who occupy them. Find out more about Healthy Homes and what this blog can do for you!

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