Household mould, black mould and mycotoxins: what the evidence says

Mould in the home looks unpleasant and can leave musty odours behind. More importantly, exposure to mould has been associated with a range of health impacts - most notably as a trigger for asthma.

But does contact with mould lead to a serious lung condition in children that has nothing to do with asthma? As it turns out, this supposed connection may not exist at all - and even if it does, it appears to be so uncommon that it is not a meaningful risk. Even so, people still often describe mould in damp homes as "toxic".

Damp, mouldy housing can damage health - just not always in the way many people assume.

What is mould?

“Mould” is a broad, everyday label for many different fungi. In discussions about damp buildings, the type that attracts the most attention is "black mould", which commonly appears as unsightly dark patches on walls and other areas affected by moisture.

Black mould is not one single organism. However, when most people use the term, they are usually referring to the fungus Stachybotrys chartarum (often shortened to S. chartarum). It is frequently listed among experts’ top ten most feared fungi.

Interest in this particular species was heightened by a report in the 1990s describing cases of haemorrhagic lung disease in several infants. This rare condition involves bleeding into the lungs and can be fatal. The report proposed that chemicals called mycotoxins, linked with this fungus, were responsible for the cluster of cases.

What are mycotoxins?

Many fungi produce mycotoxins, for defensive purposes among other roles.

There are hundreds of different compounds classified as mycotoxins. They include toxins found in poisonous mushrooms, as well as those associated with soil fungi such as Aspergillus flavus and A. parasiticus.

The fungus most often associated with black mould, S. chartarum, is capable of producing several mycotoxins. These include roridin, which can inhibit protein synthesis in humans and animals, and satratoxins, which have a wide range of toxic effects - including causing bleeding in the lungs.

Although satratoxins in particular were highlighted in the 1990s infant report, the evidence raises a number of concerns.

For a start, the quantity of mycotoxins produced by S. chartarum can vary greatly. And even where substantial amounts are present, delivering enough of these toxins into the body to cause harm is a separate issue.

Breathing in spores in contaminated (mouldy) homes is generally considered the most plausible way mycotoxins might enter the body. For example, mycotoxins have been detected in S. chartarum spores. It is also known that if mice are given direct nasal exposure to very high concentrations of spores carrying mycotoxins, some lung bleeding can occur.

However, the fact that inhalation is the most likely pathway does not mean it is a likely event.

One reason is that S. chartarum is not a prolific spore-releaser. Its spores are usually held within a slimy material, and it seldom generates the spore levels needed to reproduce the conditions used in animal experiments.

The early reports that suggested US infants with haemorrhagic lung disease had encountered toxic mycotoxin exposure were also methodologically weak.

Among the problems identified, the spore concentrations were calculated incorrectly. When these issues were later corrected, the apparent association between S. chartarum and the disease cluster essentially disappeared.

The American Academy of Asthma Allergy and Immunology notes that, while the link between damp indoor environments and harmful health outcomes is clear and well established, there is no good evidence that mycotoxins from black mould are responsible.

But mould can cause allergies

Mould can affect health in ways that do not involve mycotoxins, most often via allergic responses. A range of moulds - including black moulds - can provoke or worsen asthma attacks in people who are allergic to mould.

Less common but potentially serious reactions include allergic fungal sinusitis, allergic bronchopulmonary aspergillosis and, even more rarely, hypersensitivity pneumonitis.

These conditions can usually be managed by removing the mould (or by removing the affected person from the mould source).

People with weakened immune systems - for instance, those taking immunosuppressant medicines - may also be more susceptible to mould infections.

In a nutshell

There is enough evidence to show that mould in the home is linked with breathing problems due to its allergy-related effects.

However, there is no strong evidence that mycotoxins from household mould - and black mould in particular - are associated with major health harms.

Ian Musgrave, Senior lecturer in Pharmacology, University of Adelaide

This article is republished from The Conversation under a Creative Commons licence. Read the original article.