Heart and lungs

Can coffee machines and kettles spread toxic spores?

"Your coffee machine could be making you ill," the Mail Online reports, saying that steam released by the machine could be creating the perfect conditions for fungi to grow. The Sun reports a similar risk for kettles and showers.

But before you throw out your expensive coffee pod machine or trusty kettle, the research behind the headlines did not involve real-world conditions: it all took place in a laboratory.

Fungus is known to grow on damp wallpaper. The researchers wanted to see if fungi grown on wallpaper for several weeks at a high temperature and humidity could then produce airborne (aerosolised) fungal spores and potentially harmful toxins.

And if this did occur, they wanted to see whether the toxic particles were small enough for a person to breathe in.

Researchers did find that certain airspeeds could cause the toxins to become airborne, and some of the toxins were a small enough size to be inhaled into the respiratory tract.

The question is whether the consistently hot, moist conditions created in the lab are representative of most normal indoor living conditions.

These findings need further research – we wouldn't recommend you bin your kettle just yet.

Where did the story come from?

The study was carried out by researchers from the Université de Toulouse, the French Environment and Energy Management Agency, and the Scientific and Technical Centre for Building, Airborne Pollutants and Bioaerosol Division, all in France.

It was funded by grants from the French Ministry of Ecology, the Sustainable Development and Energy, the French Environment and Energy Management Agency, and the Scientific and Technical Centre for Building.

The study was published in the peer-reviewed journal, Applied and Environmental Microbiology.

Both the Mail Online and the Sun focus too much on the potential risks of coffee machines and kettles. These were never directly tested in the study and were only mentioned once by the lead author in a press release.

What kind of research was this?

This laboratory study aimed to look at the toxic particles (mycotoxins) produced by three different types of indoor fungus grown on wallpaper.

Mycotoxins are toxic substances produced by some types of fungi that can pose risks to human health, particularly when ingested. It's mycotoxins that make some mushrooms poisonous.

This study focused on airborne mycotoxins particles that may be small enough to breathe in.

But it's difficult to know how applicable these experimental findings are to homes, and how much of a risk to health the fungal particles may be.

What did the research involve?

The research involved three types of fungi – Penicillium brevicompactum, Aspergillus versicolor and Stachybotrys chartarum – often found in indoor environments.

They were incubated on potato sugar for two weeks at 25C to produce spore-forming cultures. Spore suspensions were then diluted and applied to wallpaper.

Small pieces of contaminated wallpaper were then placed in flasks to maintain the moisture level and incubated for a further 10 days in the darkness at 25C.

After incubation, the researchers examined the papers under the microscope. Mycotoxins became airborne when filtered humidified air (50% at 22C) was applied at a certain speed across the contaminated papers.

Sizes of the airborne particles were measured using an optical counter. The presence of mycotoxins was determined using liquid chromatography.

What were the basic results?

The researchers noticed some differences in growth and spore production of the three types of fungi on the moist wallpaper, but all three produced mycotoxins.

How did the researchers interpret the results?

The researchers concluded that fungi can produce mycotoxins small enough to be inhaled into the lungs.

They say that, "These data are important for risk assessment related to fungal contamination of indoor environments." 


This laboratory study suggests that under humid conditions, indoor surfaces like wallpaper may be colonised by fungi that produce toxic particles – some of which may be small enough to be inhaled.

But it's important that these findings aren't taken too far out of context at this stage.

The study was carried out in highly experimental circumstances where both temperature and humidity were optimised for maximal fungal growth.

We can't know for sure that these circumstances would be typical of indoor environments, even bathrooms or kitchens, if they're well ventilated.

The UK media has applied these findings specifically to coffee machines, kettles and showers, but even though these appliances produce steam, it would be wrong to single them out as they haven't even been tested. 

And the possible effects on human health also weren't tested in this study. The researchers found fungi can produce mycotoxins tiny enough to be inhaled.

But we don't know whether the concentration of toxic particles and air speeds in homes would mean people breathe in enough particles to potentially harm their health.

Fungal infections usually only pose a significant threat to the health of people with weakened immune systems or pre-existing lung conditions, such as cystic fibrosis.

As the researchers rightly say, these findings need further testing. They don't have implications for how we use household appliances at the moment.

NHS Attribution