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Claim that fungi are the sole cause of cancer misinterprets data, makes baseless assumptions

Posted on:  2024-05-16

Key takeaway

There’s no scientific evidence showing all cancers are caused by fungi. Cancer is the name for a group of diseases characterized by uncontrolled cell growth and proliferation. This occurs due to mutations that impair normal cellular “brakes” on cell growth and division. Risk factors differ from one type of cancer to another. Some cancers are associated with infectious agents like viruses, while other cancers are associated with exposure to certain chemicals.

Reviewed content


Fungi are the cause of cancer

Source: Know The Cause, Doug Kaufmann, 2024-04-30

Verdict detail

Incorrect: The current scientific consensus holds that cancer is the result of mutations that lead to uncontrolled cell growth and proliferation. There are many different risk factors for cancer, such as certain infectious agents, exposure to certain chemicals, and lifestyle choices. The assertion that all cancers can be traced to fungi is incorrect.
Misleading: While certain fungal toxins, known as aflatoxins, have been linked to liver cancer, there’s little to no evidence indicating that they increase the risk of all types of cancers.

Full Claim

Aflatoxins drive cancer development; ‘According to my hypothesis, cancer begins when the DNA from Fungus and the DNA from our white blood cells merge to form a new hybrid “tumor, or sac.” This hybrid attains a life of it’s own now, bypassing our immune defenses because it is 50% human, and therefore just enough to be recognized as “self.”’; “It is impossible to tell lung fungus from lung cancer”


On 30 April 2024, the Facebook page Know The Cause published a post implying that fungal skin infections are being confused with skin cancer, citing a 1957 “John’s(sic) Hopkins medical school textbook on Dermatology” and claiming that skin cancer cases “sometimes have a fungal beginning”.

The page, which has more than 70,000 followers, represents the eponymous television show hosted by Doug Kaufmann. Kaufmann has long propagated the belief that fungi—through the action of fungal toxins—are the cause of many diseases, including cancer. In line with this belief, he previously interviewed former physician Tullio Simoncini, who claimed cancer is caused by the fungus Candida albicans and advocated for treating cancer with sodium bicarbonate, commonly known as baking soda.

While there’s some evidence in cell cultures and mice suggesting that sodium bicarbonate can improve the effectiveness of cancer therapies[1,2], there’s none showing that sodium bicarbonate alone cures cancer in people. Simoncini was convicted of manslaughter in 2018 and sentenced to more than five years in jail, after a cancer patient whom he treated with sodium bicarbonate died.

This review focuses on Kaufmann’s claim that fungi are the cause of cancer, drawing on material published on his website Know The Cause to address the root of his claim. As we will explain below, this claim relies on misinterpreted data and baseless generalizations.

Scientific evidence links fungal toxin specifically to liver cancer, not to all cancers

On the Know The Cause website, Kaufmann claimed that fungal toxins in our food drive cancer development (“Mycotoxins are made by fungus, yet few of our healthcare providers acknowledge that fungus contributes to cancer”), singling out aflatoxin as the culprit.

This claim has a grain of truth to it. Aflatoxins, a group of toxins produced by certain fungi, are associated with an increased risk of liver cancer. This effect is mainly due to its ability to cause mutations in liver cells. The International Agency for Research on Cancer recognized aflatoxins as carcinogens in 1993.

The fungi responsible for producing aflatoxin grow on food crops like corn, soybeans, and peanuts; thus, consuming products made from these crops is one way through which people are exposed to aflatoxins.

But while the scientific evidence clearly links aflatoxins to liver cancer specifically, there’s currently little to no evidence indicating that aflatoxins are associated with a greater risk of other cancers[3]. It’s important to keep in mind that cancer isn’t a single, uniform disease, but a group of diseases that vary greatly from one another, ranging from the types of risk factors involved to how the cancer manifests.

In short, Kaufmann’s speculation that aflatoxins are responsible for cancer in general is flawed. Its underlying assumption is that aflatoxin’s known association with liver cancer risk means the toxin must also be associated with other cancers. However, Kaufmann provided no evidence to support this assumption, and the current scientific evidence hasn’t borne this out either.

Cancer cells aren’t a “hybrid” of human and fungal cells

The Facebook post’s claim that a 1957 dermatology textbook reported how skin fungal infections could be confused with skin cancer was made by Kaufmann as early as 2015, as this page on his website shows. The argument on the webpage implies that potential confusion of fungal skin infection with skin cancer means that the two are the same thing.

On the website, Kaufmann reinforced this argument with a “paper” which he claimed showed “27 lung ‘cancer’ patients who were later diagnosed with lung ‘fungus’ instead of lung cancer”, the implication being that fungal lung infections are widely misdiagnosed as lung cancer.

However, the “paper” in question—in fact a letter to the editor rather than a study—doesn’t support that implication.

The letter cited a 1997 study examining how lung infections could mimic lung cancer[4]. In a 2014 article, surgical oncologist and cancer researcher David Gorski pointed out that the study itself found that only 1.3% of lung cancer diagnoses were actually infections. 46% of these infections were due to fungi, meaning that fungi were responsible for just 0.6% of all initial lung cancer diagnoses. Far from showing that fungal lung infections are widely being mistaken for lung cancer, the finding undermines Kaufmann’s argument instead.

In the same vein, Kaufmann also asserted that lung cancer and fungal lung infections are indistinguishable from one another (“It is impossible to tell lung fungus from lung cancer”).

However, this is incorrect. Fungal cells and human lung cells are morphologically different from each other. Also, fungal cells grown in the laboratory require growth conditions and nutrients that are different from human cells. For example, fungal cells are typically grown at 30 degrees Celsius, while human cells are normally grown at 37 degrees Celsius and require incubator air to contain 5% carbon dioxide. As such, a biopsy and microbiological tests for fungi, like fungal culture, would enable clinicians to differentiate the two.

Finally, Kaufmann speculated that cancer begins when the DNA of human and fungal cells fuse together, creating a hybrid. He offered no evidence for this claim.

Gorksi explained that this scenario was implausible, pointing to gene sequencing technology that would have allowed researchers to identify fungal DNA in cancer cells as early as the 1990s, if the mechanism proposed by Kaufmann did exist.


There’s no evidence for Kaufmann’s assertion that cancer is due to a hybrid of fungal and human cells. Cancer is the name for a group of diseases characterized by uncontrolled cell growth and proliferation. This occurs due to mutations that impair normal cellular “brakes” on cell growth and division. While aflatoxins, which are produced by a particular group of fungi, have been linked to an increased risk of liver cancer, there’s little to no evidence indicating they raise the risk of other cancers. Fungi aren’t the sole cause of cancer; there are a variety of risk factors associated with different types of cancers, ranging from infectious agents to chemicals to lifestyle choices.


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