What is Black Mould?
Most people think black mould is a specific type of mould. In reality, "black mould" is simply a description of a mould's colour, not its identity.
If you've discovered black mould in your home, you're not alone. It's one of the most common reasons people contact us, but it's also one of the most misunderstood.
In my opinion, the phrase "black mould" has become almost a commercial term. It's used everywhere; by the media, landlords, contractors, homeowner, and even cleaning product manufacturers. It's become a catch-all phrase for almost any dark mould growth, giving the impression that we're dealing with one specific type of mould when, in reality, that's rarely the case.
The mould most commonly associated with the term is Stachybotrys chartarum, but many other moulds, including Cladosporium, Alternaria and some Aspergillus species, can also appear black or very dark green depending on the conditions in which they're growing.
That's why it isn't possible to identify mould accurately by colour alone.
Mould is more than something that looks or smells bad
For many people, mould is simply the black staining around a window, the patch in the corner of a bedroom or the musty smell that greets them when they walk into a room.
But mould is much more than that.
Mould is a living organism. It grows when moisture has been available for long enough to support fungal growth, making it more than just an unsightly stain on a wall. Its presence tells us something about how a building is behaving.
Rather than seeing mould as the problem itself, I prefer to see it as evidence. It's the building telling us that something isn't working as intended.
That's why understanding why mould has developed is usually far more valuable than simply identifying what colour it is.
Is black mould dangerous?
The simple answer is that it can be, but not because it's black.
Colour tells us very little about the mould itself.
Some mould species are capable of producing compounds known as mycotoxins under certain environmental conditions, while many are not. Likewise, the same mould species may appear different colours depending on where and how it has grown.
Whether mould presents a health concern depends on many factors, including:
The species present
The amount of mould
Whether spores are becoming airborne
Moisture conditions
The health and sensitivity of the occupants
The duration of exposure
Without laboratory analysis, nobody can reliably identify mould species simply by looking at it.
Why does black mould grow?
Like all mould, black mould doesn't appear by chance.
It grows because moisture is present.
That moisture may come from:
Condensation
High indoor humidity
Plumbing leaks
Roof leaks
Penetrating damp
Flooding
Building defects
The mould is simply responding to the conditions available.
If the moisture remains, the mould often returns, regardless of how many times it's cleaned.
Where is black mould commonly found?
Dark mould is often found where moisture regularly accumulates or where surfaces remain cool enough for condensation to form.
Common locations include:
Window reveals
External corners
Behind wardrobes and large furniture
Bathrooms
Kitchens
Around leaking pipework
Beneath damaged flooring
Loft timbers
Behind plasterboard
Finding mould in one of these locations doesn't automatically tell us what's causing it.
Every building behaves differently, which is why investigation is often more valuable than assumptions.
The question I think we should be asking
When people send me photographs, they often ask:
"Is this black mould?"
It's a perfectly understandable question.
But in my opinion, there's a better one.
"Why is mould growing here?"
Once you understand the source of moisture, the mould starts to make sense.
The colour becomes far less important than the conditions that allowed it to develop in the first place.
The Bottom Line
Despite its name, black mould isn't a single type of mould.
It's a commonly used term for mould that appears dark in colour, but colour alone tells us very little about the species, the potential health implications or the underlying cause.
In my opinion, we've become too focused on the phrase "black mould" and not focused enough on what the mould is trying to tell us.
Because mould isn't just something that looks unpleasant or smells musty.
It's evidence that moisture has been present, and understanding that moisture is the first step towards finding a lasting solution.
Need help understanding the cause?
Finding black mould doesn't automatically tell you what the problem is.
Whether it's caused by condensation, a hidden leak, penetrating damp or another moisture source, understanding why it's growing is the first step towards preventing it from returning.
At Mould Focus, we investigate buildings to identify the underlying causes of mould, moisture and indoor environmental conditions, providing the clarity needed to make informed decisions before any remediation begins.
Because the best solution starts with understanding the problem.