The Risks of Eating Mouldy Foods

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Recently we were asked the following questions:

“Eating mouldy bread is discouraged. Where can I find the facts that prove this? Are there moulds that grow on bread that are harmless? Some of my patients that survived food shortages in The UK during World War II by eating mouldy bread and other foods insist that such fears about mould are unfounded”.

Those are the comments/questions that we received and below we explain why eating mouldy food should be discouraged.

Why is eating mouldy food discouraged?

Rye bread contaminated with mould

Mouldy Rye bread

It is true that people may eat mouldy food without any harm. In many cases, children and adults who live on the streets in developing countries survive on food and fruits thrown into waste bins. Most of these foods and fruits are usually contaminated with mould and bacteria.

The major reasons why eating mouldy food is dangerous is because such food is likely to be contaminated with mycotoxins (i.e., fungal poisons).

Luckily, moulds that produce toxins (also called toxigenic moulds) require certain growth conditions to produce the toxins and hence presence of these moulds on food does not necessarily mean the food contains mycotoxins.

There is also a high risk of food poisoning caused by bacteria such as Staphylococcus aureus, Salmonella, Clostridium perfringens, Campylobacter, Listeria monocytogenes, Vibrio parahaemolyticus, Bacillus cereus, and Entero-pathogenic Escherichia coli.

Mycotoxin poisoning is primarily through ingestion and to some extent through contact. The effect of poisoning by mycotoxin is called mycotoxicoses. There are several documented (and probably more undocumented) cases of mycotoxicoses both in human and domesticated animals.

  • The first documented major outbreak of gangrenous ergotism is suspected to have occurred in the Rhine Valley, in 857 A.D. Numerous epidemics of ergotism followed with thousands dying as a result of the continual consumption of infected rye. Children were often the most susceptible victims.
  • In 1913, a food – borne disease called alimentary toxic aleukia occurred in Siberia. Several larger outbreaks occurred during the war years of 1941-1945 involving several districts in Western Siberia and European Soviet Russia. The disease claimed at least 100,000 people. The disease was attributed to the consumption of bread made from wheat contaminated with trichothecene mycotoxins produced by Fusarium sporotrichioides and Fusarium poae.

    A picture of Stachybotrys showing spores

  • In the 1930s in Ukraine and other parts of Eastern Europe there were outbreaks of mycotoxicoses in horses and other animals fed with hay and feed contaminated with Stachybotrys chartarum. Stachybotrys chartarum produces satratoxins (L, D, F, G and H), a class of trichothecenes which are potent inhibitors of protein synthesis in mammalian cells. Affected animals exhibited symptoms that included irritation of the mouth, throat, and nose; shock; dermal necrosis; a decrease in leukocytes; hemorrhage; nervous disorder; and death. The condition was named stachybotryotoxicosis. Stachybotryotoxicosis has also been reported in farm workers who handled contaminated hay.
  • In 1960, in England, about 100,000 turkeys and several other domestic birds died of aflatoxicosis (aflatoxin poisoning) after feeding on oil cake feed contaminated with aflatoxin, a highly potent mycotoxin produced by Aspergillus flavus and Aspergillus parasiticus.
  • In South Africa in 1970 there was an outbreak of a disease condition called equine leukoencephalomalacia after horses were fed with mouldy corn contaminated with Fusarium verticillioides. This outbreak led to the discovery of a class of mycotoxins known as fumonisins.
  • In 1974 an outbreak of aflatoxicosis in western India resulted in 397 recognized cases and 106 deaths.
  • In the summer of 1987 in India, an outbreak of gastrointestinal disorder affected thousands of residents of Srinagar and the surrounding areas in the Kashmir Valley after consuming wheat that was contaminated with both Aspergillus and Fusarium species.
  • In Kenya, in 2004 several people were hospitalized, and 125 of them died, after eating maize contaminated with Aspergillus flavus. The outbreak resulted from widespread aflatoxin contamination of locally grown maize, which occurred during storage of the maize under damp conditions.

Are there moulds that grow on food that are harmless?

Yes. In fact some moulds are used in the processing of food especially in Asian countries. The following are some of the moulds used in processing of foods.

Aspergillus flavus

Aspergillus flavus produces aflatoxins

  • Penicillium camembertii and Penicillium roquefortii are used in the production of Camembert and Roquefort types of cheese respectively.
  • Fusarium venenatum is used in the production of Quorn. Quorn is a mycoprotein (fungal protein) containing 12% protein and is used as an alternative to meat products. It contains no animal fat and cholesterol.
  • Rhizopus oligosporous. Rhizopus oligosporous is used in the production of tempeh. Tempeh is a fermented soya bean paste made by inoculating cooked soya beans with the mould Rhizopus oligosporous. This mould forms a mycelium holding the soya beans together and its extracellular proteases break down the bean protein making them digestible.
  • Aspergillus oryzae. Aspergillus oryzaeis used in processing of a number of soybean products. These include:
    • Miso, a fermented condiment made from soya beans, grain (rice or barley), salt and water. Miso production involves steaming polished rice which is then inoculated with Aspergillus oryzae and left to ferment to give an end product called koji.
    • Hamanatto, a Japanese soybean product.
    • Ket-jap, an Indonesian soy sauce.


Feeding on food or feed contaminated with mould is risky and should be avoided at all times. Eating such food could result to food poisoning either due to mycotoxin or bacterial contamination or both.

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Dr Jackson Kung'u
Dr. Jackson Kung’u is a Microbiologist who has specialized in the field of mycology (the study of moulds and yeasts). He is a member of the Mycological Society of America. He graduated from the University of Kent at Canterbury, UK, with a Masters degree in Fungal Technology and a PhD in Microbiology. He has published several research papers in international scientific journals. Jackson has analyzed thousands of mould samples from across Canada. He also regularly teaches a course on how to recognize mould, perform effective sampling and interpret laboratory results. Jackson provides how-to advice on mould and bacteria issues. Get more information about indoor mould and bacteria at

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