They are the fashionable gadgets advertised by celebrities as the must-have kitchen appliance.

But while a coffee machine may give you a welcome caffeine hit in the morning, it could also make you ill.

The steam from these machines, combined with insulated modern homes, may be exposing us to fungal toxins, it has been warned.

Making a cup of coffee in the morning adds to household damp, creating fungus which grows often unseen on our walls.

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Just walking into a room creates enough of a draught for toxic particles to escape into the air, which we breathe in deeply.

One type of toxin, which can spread when a window is opened or door slammed, has been linked to young children suffering bleeding on their lungs in the US.

These toxins may also play a role in "sick building syndrome", where people living or working in a building for many hours suffer symptoms such as asthma attacks, coughs, itchy skin and headaches.

A study published in the Journal of Applied and Environmental Microbiology determined the risk of "aerosolised particles" from fungus growing on wallpaper.

Co-author Dr Jean-Denis Bailly, from the National Veterinary School of Toulouse in France, said coffee machines "could lead to favourable conditions for fungal growth".

He said: "Coffee makers are just an example of a machine that may release steam indoors and increase the water and humidity that may help fungi to grow.

"Everything that may increase humidity may help fungi to grow since temperature and building materials are in most cases favourable."

The expert believes the trend for increasingly energy-efficient homes may aggravate the problem, as they "are strongly isolated from the outside to save energy".

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The study looked at toxins produced by different species of fungus which grow inside homes. One of these, Penicillium brevicompactum, produced toxic airborne particles in an air flow of just 0.3 metres per second, which can be produced by people moving in a room.

Stachybotrys chartarum, linked to the cases of children suffering bleeding on their lungs, released particles at six metres per second - the equivalent of the draught from a window being opened or door slamming.

Aspergillus versicolor needed a third of that air current to produce particles, which tend to be dust or tiny fragments of wallpaper to which toxins attach.

Responding to the research, David Denning, professor of infectious diseases at the University of Manchester and director of the National Aspergillosis Centre, said: "Fungal toxins (mycotoxins) can be an irritant to the eyes, throat, sinuses and lungs, and be absorbed and cause headaches.

"This study shows that these toxins can be found in the air, usually attached to dust and spores, and can be expected to be absorbed. Mould-infected wallpaper is problematic and should be removed and cleaned up, to avoid health problems."

The study also states that the toxins have been linked to "sick building syndrome", although more research is needed to determine the health effects of precise amounts of toxic particles.

The authors looked only at fungi grown on wallpaper but Dr Bailly said they can also grow on wood and painted fibreglass. Mould itself, which can be microscopic and impossible to see, is known to potentially play a part in asthma attacks and respiratory problems.