While indoor mould growth in general isn’t a commonly discussed topic in society, toxic black mould has made waves in the news over the years. Unfortunately, this has led to a long list of misconceptions. So it’s important to understand what black mould actually is, why it’s harmful, and how to identify it before it becomes a problem.


Over 100,000 species of mould have been identified by researchers so far, and they come in a variety of shapes and colours. Many of these species can be black in colour, such as Aspergillus and Chaetomium. That being said, discussions regarding black mould typically refer specifically to a species called Stachybotrys chartarum.

All species of mould reproduce by creating microscopic spores and releasing them into the surrounding area. Some species of mould, like Stachybotrys chartarum, also release microscopic toxins called mycotoxins when threatened, which are naturally toxic to the human body.

To make matters more complicated, some species of mould (including Stachybotrys chartarum) can create multiple types of mycotoxins.

Having spores and mycotoxins in your home can harm your indoor air quality and contaminate your surfaces. And since these particles are small enough to be inhaled, ingested, and absorbed into the body, they can trigger adverse health reactions.


The tricky aspect of indoor mould growth is that everyone responds differently to exposure. Adverse health effects can vary greatly from person-to-person. Genetics, length of time exposed, volume of exposure, and pre-existing conditions all play a role.

That being said, common symptoms include:

  • Brain fog and cognitive difficulty
  • Chronic fatigue
  • Allergy symptoms/persistent cold
  • Hormone imbalance
  • Digestive issues
  • Mood swings
  • Headaches and/or migraines
  • Muscle and/or joint pain


Below are four signs that you might have black mould at home:

1. Visual growth

The first and easiest way to determine if there’s indoor mould growth is to grab a flashlight and check out hot spot areas. Black mould appears black in colour, but any abnormalities could indicate contamination. Hot spot areas include:

  • Ceilings
  • Wardrobes
  • Windowsills and doorframes
  • Air vents
  • Underneath sinks
  • Inside cabinets
  • Grout and caulk
  • Toilet tank
  • Attic
  • Basement
  • Any crawlspaces

2. Water Damage

As a water-loving mould, Stachybotrys chartarum requires high levels of moisture to grow. This is why you’ll always want to check water-damaged areas for signs of black mould. Visual issues to look out for include:

  • Coffee-like stains on ceilings or walls
  • Discoloured carpeting
  • Peeling, cracked, or bubbling wallpaper
  • Peeling or bubbling paint

3. Damp Smells

If you don’t find any visible mould, that still doesn’t mean that there isn’t a problem. The growth could be in a hidden location like the inside of a wall or underneath the flooring.

In this case, rely on your sense of smell to help determine if there’s an issue. Mould growth often creates a damp, musty, earthy odour due to the release of gases called microbial volatile organic compounds (MVOC). Further, if you constantly smell dampness in the home, there’s a good chance there’s contamination.

4. Unexplained Chronic Symptoms

Sometimes, mould growth is hidden and doesn’t create an odour. In cases like this, pay close attention to your body and how you feel. Have you developed chronic symptoms over time that no doctor can pin-point a root cause for? Do they flare up any time you’re hanging out at home or in the office? Never ignore chronic symptoms or accept them as the ‘new norm.’ Instead, attempt to determine what is causing your body to send out warning signals.


Home health plays a huge role in our ongoing wellness. The safer and less contaminated these spaces are, the healthier and happier our bodies will be. Like any kind of indoor mould, black mould should be avoided and prevented as much as possible. Once you notice these tell-tale signs of mould, it’s time to spring into action and get rid of it – or move. Then work on your treatment plan.