Aflatoxins: The Only Mycotoxin Classified as a Definite Human Carcinogen
Aflatoxins are produced by Aspergillus flavus and Aspergillus parasiticus, mainly on stored nuts, maize and spices. Aflatoxin B1 is the most potent naturally occurring liver carcinogen identified, and it is the only mycotoxin group the International Agency for Research on Cancer places in Group 1, carcinogenic to humans. Exposure is overwhelmingly dietary rather than environmental.
Mainly dietary
Aflatoxin is a food storage problem, not a building problem. A result here points at the pantry and the supply chain behind it, not at a damp wall.
Which fungi produce aflatoxins
The principal producer, generating aflatoxins B1 and B2 on crops before and after harvest.
Produces the G-series aflatoxins in addition to the B-series, and is more common in groundnut-growing regions.
Where exposure comes from
A urine panel confirms that a compound reached you. It cannot say by which route. These are the realistic possibilities, which is what a result has to be read against.
Peanuts, pistachios, almonds and brazil nuts are among the most consistently affected commodities, particularly where drying and storage are poorly controlled.
A staple exposure route in regions where maize is a dietary mainstay and storage is warm and humid.
Chilli, paprika, black pepper and dried figs are routinely monitored for aflatoxin in import controls.
Aflatoxin M1 is the hydroxylated metabolite excreted in the milk of animals fed contaminated feed, which is why it is regulated separately.
Inhalation exposure is documented in grain handling and processing, though it is a minor route compared with diet.
How it affects the body
Aflatoxin B1 is not itself the damaging agent. Cytochrome P450 enzymes in the liver, chiefly CYP3A4 and CYP1A2, oxidise it to aflatoxin B1-8,9-epoxide, an extremely reactive intermediate. Bioactivation by the liver is why the liver is the organ harmed.
That epoxide binds covalently to the N7 position of guanine in DNA, forming an adduct. If the adduct is not repaired before replication, it produces a characteristic G to T transversion.
The signature consequence is a specific mutation at codon 249 of the TP53 tumour suppressor gene, which is found at high frequency in liver cancers from high-aflatoxin regions and rarely elsewhere. Few carcinogens leave a molecular fingerprint this specific.
Chronic hepatitis B infection multiplies the risk substantially rather than adding to it, and the interaction between the two is one of the clearest examples of synergy in cancer epidemiology.
Documented health effects
Hepatocellular carcinoma is the principal concern. Aflatoxin exposure is an established cause, with risk rising sharply in people who are also chronically infected with hepatitis B.
High-dose exposure causes acute liver failure. Documented outbreaks following consumption of heavily contaminated maize have carried high mortality.
Chronic exposure in early childhood is associated with impaired growth in several population studies, though the mechanism is not fully settled.
Suppression of cell-mediated immunity is reported in both animal and human studies.
Cancer classification: IARC Group 1, carcinogenic to humans
How it is measured
Urine panels typically measure aflatoxin M1, the hydroxylated metabolite excreted after B1 is metabolised. It reflects recent intake, over roughly the preceding day or two, rather than long-term exposure.
The aflatoxin B1-lysine adduct in serum albumin is the superior biomarker for chronic exposure, integrating intake over two to three months. It is standard in research biomonitoring but uncommon on consumer panels.
Because the urinary metabolite clears quickly, a single negative urine result does not exclude meaningful long-term exposure. This is the opposite of the situation with ochratoxin A.
The wider question of what these panels can and cannot establish is covered in the guide to mycotoxin urine testing.
Reading a aflatoxins result
A detected aflatoxin metabolite indicates recent dietary intake. It is not a marker of building contamination, and remediating a house is not a coherent response to it.
The practical follow-up is dietary rather than environmental: nuts and nut butters, maize products, spices and dried fruit, with attention to storage conditions and sourcing.
Interpret a negative result cautiously. The urinary metabolite has a short window, so absence on one sample reflects the last day or two rather than the last year.
If you are holding a panel and want each value explained, the free lab report interpreter reads mycotoxin results alongside ERMI and HERTSMI-2 building scores and the inflammatory markers used in biotoxin illness, and explains what each one indicates.
Frequently asked questions
What does aflatoxin M1 in urine mean?
Aflatoxin M1 is the metabolite your liver produces from aflatoxin B1, and finding it in urine indicates dietary intake over roughly the preceding one to two days. It is a short-window marker, so it reflects recent food rather than cumulative exposure and says nothing about your building.
Which foods carry the most aflatoxin risk?
Groundnuts and tree nuts, maize and maize products, spices such as chilli and paprika, and dried figs. Milk can carry aflatoxin M1 where dairy animals have been fed contaminated feed. Risk depends heavily on how the commodity was dried and stored rather than on the food itself.
Why are aflatoxins classified as Group 1 when other mycotoxins are not?
Group 1 requires sufficient evidence of carcinogenicity in humans, and aflatoxin has it: consistent epidemiology linking exposure to liver cancer, a defined mechanism of DNA adduct formation, and a characteristic TP53 mutation found in tumours from high-exposure regions. Ochratoxin A, by comparison, sits in Group 2B on weaker human evidence.
Can I get aflatoxin exposure from a mouldy house?
It is not the typical route. Aspergillus flavus is primarily a crop and storage organism rather than a building coloniser, so aflatoxin exposure is overwhelmingly dietary. Inhalation is documented in occupational grain handling but is a minor contributor for most people.
Screening for Biotoxin Effects
A mycotoxin result describes what your body is clearing. The Visual Contrast Sensitivity test measures something different, a neurological effect associated with biotoxin exposure, which gives a second and independent data point. Free, in your browser, about 15 minutes.