Rain in Sydney has led to an outbreak of mould, particularly in cheaper rental properties, with profound and insidious impacts on health. By Sarah Price.

Households battling toxic mould after record rains

A man walks through the Sydney rain earlier this month.
A man walks through the Sydney rain earlier this month.
Credit: Hu Jingchen / Xinhua News Agency via Getty Images

When the rain began falling in late February and early March, and falling, Sydney was forced inside. People shut up their homes. The weather system lasted days and days. It brought torrential rain and flooding. It produced record levels of humidity and created the perfect breeding ground for mould.

In some rentals it was thick and black on the walls. People reported struggles with their landlords for adequate ventilation or to fix roofs and gutters. Mould grew on doors, on cupboards, on the walls, across the ceiling.

There are thousands of species of mould. It loves the wet, the damp, the dark. It thrives in poorly ventilated rooms and buildings and begins to grow in conditions of 65 to 70 per cent humidity. During Sydney’s recent rains, levels of humidity in an average home were at 90 to 95 per cent.

Adequate insulation, heating and cooling, and appropriate ventilation to reduce humidity levels and condensation, are all required to eliminate or minimise mould inside the home. Roofs, walls, flooring, skylights and windows need to be watertight to control leaks and maintain drainage. In the absence of an airconditioner or dehumidifier, homes in areas of high humidity are almost certain to be damp.


Elizabeth is a single parent living in Greater Sydney. She has lived with her two children in the same rental property for more than five years. The house has always been mouldy, she says, but the recent weather has increased the problem. Mould has grown over every interior door, on walls, on living room furniture. It has grown on woven storage baskets and the children’s beanbag and on clothes in their wardrobes.

At Elizabeth’s house there are gaps in the floorboards. There is no airconditioning. Two windows are locked open. She runs an upright fan to keep the air moving and when it’s not too hot she turns the heater on to dry the washing. Recently mould has appeared on furniture in the bedrooms. At night her children sometimes appear in her room to complain that their beds are damp. Elizabeth and her children have been more tired than usual, “but luckily we have no respiratory issues”.

“I haven’t contacted the real estate because they don’t really do much,” she says. “They will repair urgent stuff, like a sewer leak, but other things they don’t worry about. A couple of years ago water started coming in the window frame and running down the interior wall and they wanted a photo, and that was it … So I haven’t bothered to tell them about this.”

Five years is a long time in a rental, Elizabeth says. She is not prepared to risk her tenure by making complaints. “I am a bit nervous about it. I don’t want to activate anything that will make them tell me I can’t live here anymore. Rent prices are astronomical now. It is very hard to find a place for starters, let alone a place you can afford. That is also why I don’t complain.

    “After dealing with the pandemic this feels like another thing to navigate. I went to Penrith to get a dehumidifier and they were all sold out. So now I am on a waitlist. I am lucky I do have the money to buy it when they come back in stock, though. Other people who are renting might not be able to afford that.”


Christabelle Yeoh is a doctor at Next Practice GenBiome in Sydney’s Edgecliff and a member of Toxic Mould Support Australia. Context is important to Yeoh’s work and she has a keen interest in environmental medicine. She sometimes treats her patients in tandem with a building biologist. The biologist can undertake mould auditing, humidity readings and indoor allergen testing.

Yeoh explains that Bau Biologie, or building biology, is the practice of building safe homes. It began in Germany with the idea that the health of the building you live in reflects your health. “Medical testing of a sick person alone is not always sufficient to give you clues to their illness,” she says. “Testing their environment is sometimes needed.”

Yeoh tells The Saturday Paper that exposure to mould can have profound effects on health. Mould will mimic any kind of allergy that affects the upper respiratory tract. “The effects of mould exposure are insidious. Most commonly it affects the mucosal system where air and mould toxins hit the body: eyes, nose, throat, lungs. It could be watering eyes, congested sinuses, cough, breathlessness, wheeze – what might look like asthma.”

One of the difficulties with mould is that it is invisible to both practitioners and to the patient, Yeoh says. When a patient presents with a cough, irritation, breathlessness or sinus congestion, the mould exposure won’t be seen on an X-ray or in the results of a blood test. A patient may be treated for asthma and required to use a Ventolin inhaler, which will help somewhat, but what if there is an environmental cause or trigger that could be removed? The symptom may be treated with a drug that does work but the cause is never unearthed and the person’s problem may increase.

The symptoms of mould exposure are not necessarily immediate and people usually complain of more than one thing, Yeoh says. Mould exposure can cause rashes, fatigue, headaches, constipation, diarrhoea and bladder irritability. It can present like chronic fatigue syndrome or anxiety. “For some people mould exposure can cause significant anxiety. There is a higher level of biological arousal detected by the nervous system. People can become hyper alert – they might feel not quite right. It is one of the conditions in the mental health space when people have chronic anxiety that is really easy to miss, because you wouldn’t think of environmental exposure as causing anxiety.”

Yeoh continues: “Chronic or prolonged exposure to mould can affect the autonomic nervous system – the system that conducts your heartbeat and your blood pressure. It could present as fatigue because your heart beats faster than usual, or your blood pressure is lower than usual. It could be headaches because of inflammation in the brain’s immune system, the microglia. It could be loss of memory or difficulty concentrating, almost like early cognitive decline because the brain is not firing on all cylinders. It is like a slowing down of the whole neurological system. When it is really severe – which isn’t common – it could be confusion, twitches, tremors, or partial or pseudo seizures.

“In rare cases, in someone with an immune deficiency, the mould spores might get caught in their lungs and cavitate there and grow. When it is that bad the mould can be seen on an X-ray.”

Mould exposure is a common problem in old or poorly built dwellings, Yeoh says. Leaking roofs and pipes, and damp, are not always visible. If water damage is not dried out within 48 hours, you can get damp going through the walls and carpets.

“That, coupled with humidity because of the recent rains, means a waterlogged building would have zero chance of drying out. The mould that grows through damp is just rampant, particularly with cheaper building materials,” she says. “MDF and chipboard is like junk food to mould. It eats through it very fast. People in lower socio-economic areas are likely to have that kind of housing and are easily affected.

“You could have mouldy bed frames, headboards, side cupboards – and people are sleeping in those environments.”


The results of a study released this week by tenant advocacy group Better Renting found that people who rent generally live in lower-quality housing. Rental properties tend to be in worse states of repair and have poorer energy efficiency. Renters have fewer options to stay cool and to dry out the air in their home. They are less likely to have airconditioning. If they do have it, they are less likely to use it due to cost concerns.

In general, people who rent earn less than others. People living below the poverty line are disproportionately renters.

The report showed that a healthy home was one in which indoor temperatures remain within a comfortable range. Prolonged high temperatures impact negatively on a renter’s mental and physical health – due not only to the stress of heat or humidity but to the renter’s powerlessness or lack of agency in managing the problem.

Property investors currently have minimal legal obligations to reduce the negative impacts of heat. No Australian jurisdiction has explicit requirements for cooling infrastructure including airconditioning, ceiling fans, or even flyscreens on windows. The report recommends that minimum energy efficient standards be established for rental properties. If investors were required to make the necessary improvements to their property – through ventilation, insulation or airconditioning – rental homes could be more easily kept at healthy temperatures.

Renters and people on low incomes are already suffering disproportionately from more extreme and frequent weather events. This will be exacerbated as the effects of climate change worsen. Physical and mental hardships endured by people who rent will be intensified by increased heat and humidity, fires, storms, heavy rainfall and flooding.

For Elizabeth, the past few days have been spent cleaning and airing her home, trying to eliminate the mould with vinegar and oil of cloves. She has had to throw out furniture, luggage and craft supplies.

“I think I’m on top of it then I pick something up or walk past something and find more mould,” she says. “Trying to get rid of it is just part of my daily routine now, like brushing my teeth.”

This article was first published in the print edition of The Saturday Paper on March 19, 2022 as "Breaking the mould".

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