Is black mould really as bad for us as we think? A toxicologist explains
- Written by The Conversation
Mould in houses is unsightly and may cause unpleasant odours. More important though, mould has been linked to a range of health effects – especially triggering asthma.
However, is mould exposure linked to a serious lung disease in children, unrelated to asthma? As we’ll see, this link may not be real, or if it is, it’s so rare to not be a meaningful risk. Yet we still hear mould in damp homes described as “toxic”.
Indeed, mouldy homes can harm people’s health, but not necessarily how you might think.
What is mould?
Mould is the general term for a variety of fungi. The mould that people have focused on in damp homes is “black mould”. This forms unsightly black patches on walls and other parts of damp-affected buildings.
Black mould is not a single fungus. But when people talk about black mould, they generally mean the fungus Stachybotrys chartarum or S. chartarum for short. It’s one of experts’ top ten feared fungi.
The focus on this species comes from a report in the 1990s on cases of haemorrhagic lung disease in a number of infants. This is a rare disease where blood leaks into the lungs, and can be fatal. The report suggested chemicals known as mycotoxins associated with this species of fungus were responsible for the outbreak.
What are mycotoxins?
A variety of fungi produce mycotoxins to defend themselves, among other reasons.
Hundreds of different chemicals are listed as myocytoxins. These include ones in poisonous mushrooms, and ones associated with the soil fungi Aspergillus flavus and A. parasiticus.
The fungus typically associated with black mould S. chartarum can produce several mycotoxins. These include roridin, which inhibits protein synthesis in humans and animals, and satratoxins, which have numerous toxic effects including bleeding in the lungs.
While the satratoxins, in particular, were mentioned in the report from the 90s in children, there are some problems when we look at the evidence.
The amount of mycotoxins S. chartarum makes can vary considerably. Even if significant amounts of mycotoxin are present, getting them into the body in the required amount to cause damage is another thing.
Inhaling spores in contaminated (mouldy) homes is the most probable way mycotoxins enter the body. For instance, we know mycotoxins can be found in S. chartarum spores. We also know direct injection of high concentrations of mycotoxin-bearing spores directly in the noses of mice can cause some lung bleeding.
But just because inhaling spores is the probable route of contamination doesn’t mean this is very likely.
That’s because S. chartarum doesn’t release a lot of spores. Its spores are typically embedded in a slimy mass and it rarely produces the spore densities needed to replicate the animal studies.
The original reports suggesting the US infants who were diagnosed with haemorrhagic lung disease were exposed to toxic levels of mycotoxins were also flawed.
Among other issues, the concentrations of mould spores was calculated incorrectly. Subsequent correction for these issues resulted in the association between S. chartarum and this disease cluster basically disappearing.
The American Academy of Asthma Allergy and Immunology states while there is a clear, well-established relationship between damp indoor spaces and detrimental health effects, there is no good evidence black mould mycotoxins are involved.
But mould can cause allergies
Moulds can affect human health in ways unrelated to mycotoxins, typically through allergic reactions. Moulds including black moulds can trigger or worsen asthma attacks in people with mould allergies.
Some rarer but severe reactions can include allergic fungal sinusitis, allergic bronchopulmonary aspergillosis and rarer still, hypersensitivity pneumonitis.
These can typically be controlled by removing the mould (or removing the person from the source of mould).
People with impaired immune systems (such as people taking immune-suppressant medications) may also be prone to mould infections.
In a nutshell
There is sufficient evidence that household mould is associated with respiratory issues attributable to their allergic effects.
However, there is no strong evidence mycotoxins from household mould – and in particular black mould – are associated with substantial health issues.
