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Causes of Black Mould

/ 7 min read

Black mould (also known as toxic black mould) is one of the most well known toxic moulds and can cause respiratory discomfort and serious health problems. 

Here is our helpful guide about the causes of black mould, where it grows and what to do when you find it.

What is Black Mould? 

Toxic black mould (or Stachybotrys Chartarum) classifies as a fungus because of its ability to eat its way through organic material by releasing mycotoxin spores to break down the material. As a living organism, black mould grows on damp, moist surfaces, areas with high levels of water damage or with naturally high moisture levels, or where there is inadequate ventilation.

The mycotoxin spores of black mould can travel airborne around the home, appearing greenish-black in colour with a lingering musty smell. It can appear on the walls, furniture, bathroom tiles and window sills, making it difficult to control and eradicate. Because the spores are invisible to the human eye, it is easy to frequently inhale them without noticing.

What causes Black Mould

The ideal conditions for black mould growth are within warm, damp places and a temperature of around 21°C. Here are some likely causes for mould in your home and property: 

Water Damage: 

If your home is prone to high levels of moisture, season flooding or is subject to water damage, mould can begin to grow within 48 hours. Some common areas of the home that may be affected by leaking pipes, blocked gutters and plumbing issues include: 

  • Between walls 
  • Basements 
  • Garages 
  • Carpets or underlay 
  • Skirting boards 

Make sure that you clean and dry all leaks and spills or seek out a professional for larger water damage services


Naturally high levels of humidity make it extremely difficult for moisture control. Mould can easily grow on clothes and around the home even if there is plenty of natural light and air circulation. This is why dehumidifiers are necessary for sub-tropical locations to help extract the moisture from the air and control the humidity levels.

If you are using a dehumidifier or air-conditioner to help regulate moisture levels, make sure to regularly clear out excess water trays and seek out a professional to clean and sanitise your air-conditioning unit. 

Moisture build-up and inadequate ventilation: 

With high levels of condensation and moisture, bathrooms and kitchens are at a high risk of mould growth when steam circulates the space – especially if there is inadequate ventilation. 

Using ventilation fans or circulating the air will help regular the airflow throughout the area and prevent moisture buildup. You can open the window to let the air escape or exhaust fans to stop the moisture from rising. 

Where does Black Mould Grow? 

Black mould in bathrooms: 

Bathrooms with inadequate ventilation create the perfect environment for black mould growth. You can commonly find it growing in between bathroom tiles, around the bath or on the shower curtain and can easily spread up the walls and onto the ceiling without rapid treatment. 

Black mould in kitchens:

Black mould growth in the kitchens is likely the result of moisture buildup as a result of steam, cooking or condensation. If the moisture has nowhere to go, it will linger and cause mould to spread around kitchen appliances, taps or under the sink. 

Aside from inadequate ventilation, it can also be a result of a larger problem such as plumbing issues or a persisting leak. 

Black mould in carpet: 

Carpets are another common area for black mould growth and can attach to the dust and moisture that accumulates in carpets. This usually occurs in dark or damp areas around the house. If you suspect your carpet contains black mould, it is recommended to seek out the assistance of a professional mould removal service for an inspection. 

Can Black Mould Affect Your Health? 

If you frequently inhale mycotoxin spores, it may cause respiratory discomfort in the upper tract and cause more serious health problems. This is especially the case with those with existing respiratory issues, in children and the elderly. Some common symptoms of inhaling black mould spores may include:

  • Headaches
  • Coughing
  • Sneezing 
  • Dizziness 
  • Fever 

In more severe cases, black mould can also cause: 

  • Vomiting
  • Nausea 
  • Respiratory complications 

Overexposure to black mould disrupts the overall air quality and heighten the risk of either developing or exacerbating existing health problems. This may include the onset of allergies or asthma symptoms in those with pre-existing conditions and weakened immune systems. 

How to Manage Black Mould? 

Black mould thrives on moisture to grow and spread. Here are some of the most effective ways to manage black mould: 

  • Use a dehumidifier – especially in sup-tropical locations 
  • Ensure your bathroom is well ventilated 
  • Keep all areas of the home dry 
  • Circulate the air regularly – especially in dark damp areas
  • Clean and dry floods, spills or water damage within 48 hours 
  • Regularly clean out external drainage, guttering, downpipes and eaves 
  • Hang damp clothes out to dry outside 
  • Cover pans when cooking 

When to Call a Mould Removal Professional? 

Black mould may cause serious health problems if it is left untreated. If you suspect black mould is growing around your home or property it is important to take immediate action to eradicate the infestation. 

If you are afraid of mould becoming a problem in your home and are looking for a long-term solution, be sure to call upon a professional team to help you. The MouldMen team will inspect, treat, and provide you with a Mould Management and Prevention Plan to ensure that your home is kept safe and free from mould. Call us on 1300 60 59 60 to book your free inspection today.

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