Black mould in homes: what the health evidence shows

Mould in the home looks unpleasant and can create bad smells. More importantly, it has been associated with several health effects, particularly as a trigger for asthma.

But can exposure to mould cause a serious childhood lung condition that is separate from asthma? As the evidence shows, that connection may not exist; if it does, it is so uncommon that it does not represent a significant risk. Even so, mould in damp homes is still often labelled “toxic”.

Mouldy housing can certainly affect health, although not always for the reasons people assume.

What is mould?

Mould is a broad name for various fungi. In damp buildings, the type that attracts the most attention is “black mould”, which appears as unattractive dark patches on walls and elsewhere in areas affected by damp.

Black mould is not one specific fungus. However, when people use this term, they usually mean the fungus Stachybotrys chartarum, or S. chartarum for short. It is included among experts’ ten most feared fungi.

Interest in this species arose from a 1990s report describing haemorrhagic lung disease in several infants. In this rare and potentially fatal illness, blood enters the lungs. The report proposed that the outbreak was caused by chemicals called mycotoxins linked with this fungus.

What are mycotoxins in black mould?

Fungi make mycotoxins for several purposes, including self-defence.

Hundreds of chemicals are classified as mycotoxins. They include compounds found in poisonous mushrooms as well as those linked to the soil fungi Aspergillus flavus and A. parasiticus.

The fungus most commonly connected with black mould, S. chartarum, is capable of producing several mycotoxins. These include roridin, which disrupts protein production in people and animals, and satratoxins, which have many toxic effects, including bleeding in the lungs.

Satratoxins in particular were referred to in the 1990s report involving children. However, the evidence has problems when examined more closely.

The quantity of mycotoxins produced by S. chartarum can differ greatly. And even where substantial quantities are present, that does not mean they enter the body at the level needed to cause harm.

Breathing in spores in contaminated, mouldy homes is the most likely way for mycotoxins to get into the body. For example, mycotoxins have been identified in S. chartarum spores. It is also known that directly administering high concentrations of mycotoxin-carrying spores into mice’s noses can lead to some bleeding in their lungs.

Yet the fact that inhaling spores is the likely exposure route does not make such exposure especially probable.

This is because S. chartarum does not shed large numbers of spores. Its spores are generally trapped within a slimy material, and the fungus seldom reaches the spore concentrations required to reproduce the animal-study findings.

The original reports claiming that US infants diagnosed with haemorrhagic lung disease had encountered toxic mycotoxin levels were also flawed.

For one thing, the mould-spore concentrations were calculated wrongly. Once these problems were corrected, the apparent association between S. chartarum and this cluster of illness virtually vanished.

The American Academy of Asthma Allergy and Immunology says that, although damp indoor environments have a clear and established link with harmful health effects, there is no sound evidence that black mould mycotoxins play a part.

But mould can cause allergies

Mould can influence health independently of mycotoxins, most often by causing allergic responses. Moulds, including black moulds, may bring on or aggravate asthma attacks in people who are allergic to mould.

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

These conditions can usually be managed by removing the mould, or by taking the affected person away from the source of mould.

People with weakened immune systems, such as those using immune-suppressant medicines, may also be more susceptible to mould infections.

In a nutshell

There is enough evidence to link household mould with respiratory problems caused by its allergic effects.

However, there is no strong evidence that mycotoxins from household mould - especially black mould - are connected with significant 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.