Mould in homes: what black mould and mycotoxins mean for health

Mould in homes looks unpleasant and can leave musty odours behind. More importantly, mould exposure has been associated with a range of health effects - particularly the triggering of asthma.

But does exposure to mould have any connection with a severe lung illness in children that is not asthma-related? As the evidence shows, either that connection is not genuine or, if it exists at all, it is so uncommon that it does not represent a meaningful risk. Even so, mould in damp properties is still sometimes labelled “toxic”.

There is no doubt that living with mould can affect health - just not always in the way people assume.

What is mould?

“Mould” is a catch-all term for many different fungi. The type most often discussed in damp homes is “black mould”, which appears as conspicuous dark patches on walls and other areas of buildings affected by moisture.

Despite the name, black mould is not one single fungus. In everyday use, however, “black mould” usually refers to Stachybotrys chartarum (often shortened to S. chartarum), a species that features on many experts’ lists of the ten most feared fungi.

Attention on this particular species largely stems from a 1990s report 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.

What are mycotoxins?

Many fungi produce mycotoxins, in part as a means of self-defence.

There are hundreds of different compounds classed 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 commonly linked with black mould, S. chartarum, is capable of producing several mycotoxins. These include roridin, which blocks protein synthesis in humans and animals, and satratoxins, which can cause a wide range of toxic effects, including bleeding in the lungs.

Although satratoxins in particular were highlighted in that 1990s report involving children, the overall evidence raises several concerns.

To begin with, the quantity of mycotoxins produced by S. chartarum can differ markedly. And even when substantial levels are present, a separate question is whether enough of those toxins can actually enter the body to cause harm.

Breathing in spores in contaminated (mouldy) homes is the most likely pathway for mycotoxins to get into the body. For example, mycotoxins have been identified in S. chartarum spores. We also know that giving mice direct, high-dose exposure - by injecting large concentrations of mycotoxin-bearing spores straight into their noses - can produce some bleeding in the lungs.

However, the fact that inhalation is the most plausible route does not mean it is especially probable in real homes.

One reason is that S. chartarum is not a heavy spore-shedder. Its spores are usually held within a slimy material, and it seldom generates the spore densities required to mirror the animal experiments.

The early reports implying that US infants with haemorrhagic lung disease had been exposed to toxic mycotoxin levels were also methodologically weak.

Among other problems, the mould spore concentrations were worked out incorrectly. Once those errors were addressed, the purported association between S. chartarum and the disease cluster effectively vanished.

The American Academy of Asthma Allergy and Immunology notes that, although there is a clear and well-established link between damp indoor environments and harmful health outcomes, there is no solid evidence that black mould mycotoxins are the cause.

But mould can cause allergies

Mould can still affect people in ways that have nothing to do with mycotoxins, most commonly via allergic responses. Moulds - including black moulds - can provoke or aggravate asthma attacks in individuals who are allergic to mould.

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

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

People with weakened immune systems (for instance, those taking immunosuppressant medicines) may also be vulnerable to mould infections.

In a nutshell

There is enough evidence to show that household mould is linked with respiratory problems that are attributable to allergic effects.

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

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.