A 2026 analysis applied a new extraction method to 63 edible mushroom samples across six species and found that every single sample contained at least one of four Alternaria toxins. The reason nobody knew this before is stated plainly in the paper: the lack of reliable detection methods had left contamination data for mushrooms severely limited. Which means the certificate of analysis on your powder was never testing for it.
Mycotoxins are made by moulds — Aspergillus, Penicillium, Fusarium, Alternaria — that grow on a crop during drying and storage, not by the mushroom itself. In 60 medicinal herbal products from the Czech market, 40% contained quantifiable ochratoxin A up to 826.62 ng/g and 27% contained citrinin up to 472.79 ng/g, with both present together in six product types. In 63 mushroom samples from six species, all carried at least one Alternaria toxin, most commonly tentoxin (76.2% of samples) and alternariol (55.6%), with shiitake particularly prone to tentoxin. Mycotoxins are heat-stable and survive hot-water extraction, so a concentrated extract concentrates them alongside the actives. Routine certificates test heavy metals and microbial counts, which measure neither.
This is not an argument against mushroom supplements. It is an argument about which question a quality document is answering, and about a gap between what is tested and what is present.
Mushrooms Are Fungi — So What Does "Mould-Free" Mean?
It is a category error worth clearing up first. A mushroom is the fruiting body of a fungus, so a product containing no fungal material would contain no product.
The contamination that matters comes from different fungi: filamentous moulds that colonise the harvested material while it is being dried, transported or stored, and which secrete toxic secondary metabolites as they do. The genera responsible are the same ones that contaminate grain, spices and nuts.
So the risk is a handling and storage question rather than a biology-of-mushrooms question, which is good news: it is controllable, and the controls are known.
What Has Actually Been Measured
Two datasets, from different angles.
Toman's 2025 study bought 60 medicinal herbal products on the Czech market during 2020–2021 and assayed them for ochratoxin A and citrinin by HPLC with fluorescence detection and immunoaffinity clean-up. Forty per cent of samples were above the limit of quantification for ochratoxin A, reaching 826.62 ng/g, and 27% for citrinin, reaching 472.79 ng/g. Both toxins were present together in six product types.
Zhao's 2026 study is the mushroom-specific one. Using a hydrophilic-lipophilic solid-phase microextraction fibre with detection limits between 0.01 and 0.26 µg/kg, the team analysed 63 edible mushroom samples from six species. Every sample contained at least one of alternariol, alternariol monomethyl ether, altenuene or tentoxin. Tentoxin was detected in 76.2% of samples and alternariol in 55.6%, and contamination patterns varied by species — Lentinula edodes was prone to tentoxin, Pleurotus eryngii to alternariol and tentoxin together.
The concentrations here are genuinely low, in the microgram-per-kilogram range, and it would be alarmist to present them otherwise. The finding is ubiquity, not toxicity.
Why Extraction Makes It Worse, Not Better
Here is the part that inverts most people's assumption. Mycotoxins are small, heat-stable molecules. Hot-water extraction does not destroy them and alcohol extraction does not exclude them.
Now apply the arithmetic of an extract ratio. A nominal 10:1 extract concentrates ten units of raw material into one unit of product. Whatever mycotoxin burden those ten units carried does not disappear at the point of concentration — it arrives in one unit of finished powder.
So a concentrated extract is plausibly a higher per-gram mycotoxin exposure than the dried mushroom it was made from, which is the exact opposite of the intuition that extracts are the purified option. Kanabus's 2025 review reaches the same conclusion for the wider supplement category, singling out concentrated plant extracts as potential sources of multi-mycotoxin exposure. Our extract ratios article covers why that ratio number is doing so much unexamined work.
The Co-Occurrence Problem
Individual concentrations in the published surveys are typically low to moderate. The reason toxicologists are nonetheless uneasy is that multiple toxins commonly appear together in a single product.
Regulatory limits are generally set one analyte at a time, and exposure assessment is usually performed the same way. A product carrying four toxins each at a third of its own limit passes every individual test and has never been evaluated as the combination it actually is.
That is a live research gap rather than a demonstrated harm, and it is the main reason this topic is worth following rather than dismissing.
What a Certificate of Analysis Usually Covers
| Test | What it detects | Covers mycotoxins? |
|---|---|---|
| Heavy metals panel | Lead, cadmium, arsenic, mercury | No — unrelated contaminant class |
| Total plate count, yeast and mould count | Live organisms present now | No — toxins persist after the mould dies |
| Beta-glucan assay | Active content | No |
| Aflatoxin panel | Aflatoxins B1, B2, G1, G2 | Partly — one genus only |
| Ochratoxin A | OTA specifically | Partly — the one with EU limits for herbs |
| Alternaria toxins | Alternariol, tentoxin and relatives | Almost never tested |
The yeast and mould count deserves a specific note, because it is the test people assume covers this. It counts viable organisms. Mycotoxins are chemical residues that remain long after the mould producing them has been killed by drying or heat, so a clean mould count is entirely compatible with a contaminated product.
What Regulation Exists
The EU sets maximum levels for aflatoxins and ochratoxin A in various foods, and new ochratoxin A limits for herbs came into force during the period covered by the Czech study. That framework is why OTA is the mycotoxin most likely to have been tested in a European supplement at all.
What it does not cover well is the Alternaria group, where limits remain incomplete or inconsistent across the category, and emerging mycotoxins more broadly. Reviewers in this field consistently name harmonised limits and routine monitoring as the missing pieces.
Storage Is the Part You Control
Mould growth needs moisture. Dried mushroom material that is properly dried, sealed and kept cool does not support it; material that is under-dried, stored warm or repeatedly opened in a humid kitchen does.
That makes home storage a real variable rather than a footnote, particularly for bulk purchases of dried mushrooms or chunks kept for a year or more. Our guide to storing mushroom extracts and powders covers the practical side; the relevant point here is that a product can leave a clean supply chain and become a problem in your cupboard.
What to Do
- Ask which mycotoxins were tested, by name. "Tested for purity" and a yeast and mould count are not answers to this question.
- Treat ochratoxin A as the minimum. It has EU limits for herbs, so a European supplier has the least excuse for not having it.
- Understand that a mould count is not a mycotoxin test. Toxins outlive the organisms that made them.
- Be more, not less, sceptical of concentrated extracts. Concentration carries the contaminant load forward with the actives.
- Buy quantities you will finish. A kilogram of dried material stored for two years in a kitchen is the highest-risk thing in this article.
- Store airtight, cool and dark, and never return damp material to the bag. Moisture is the single variable mould needs.
- Discard anything with a musty smell or visible bloom. Sorting out the good bits is not a valid strategy with a diffusible metabolite.
The Honest Summary
The measured concentrations in mushrooms are low, no case of harm from mycotoxins in a mushroom supplement has been published, and nothing here should stop anyone taking a well-sourced product. That is the fair proportion.
What the recent data change is the assumption of absence. When a method capable of finding Alternaria toxins was finally applied to mushrooms, it found them in 100% of samples, and the adjacent herbal supplement category shows ochratoxin A above the limit of quantification in 40% of products. Meanwhile the documents buyers rely on test heavy metals and live organisms, neither of which measures this, and the extraction step that is supposed to purify a product concentrates the residue instead. Ask for the analyte names. The answer you get tells you what kind of supplier you are dealing with.
Frequently Asked Questions
Can mushroom supplements contain mycotoxins?
Yes, from moulds that grow on the material during drying and storage rather than from the mushroom itself. In one 2026 analysis, all 63 mushroom samples across six species contained at least one Alternaria toxin, most often tentoxin or alternariol.
Does a yeast and mould count prove a product is safe?
No. That test counts living organisms, while mycotoxins are chemical residues that persist after the mould has been killed by drying or heat. A clean count is entirely compatible with measurable toxin content.
Does extraction remove mycotoxins?
No. They are small, heat-stable molecules that survive hot-water extraction, and a concentrated extract carries forward the burden of all the raw material it was made from — so per gram, an extract can contain more than the dried mushroom it came from.
Which mycotoxins should a certificate of analysis show?
Ochratoxin A at minimum, since the EU sets limits for it in herbs, and ideally aflatoxins as well. Alternaria toxins are almost never tested despite being the group found in every mushroom sample in the 2026 survey.
How should I store dried mushrooms to prevent mould?
Airtight, cool, dark and dry, in quantities you will actually finish. Mould needs moisture, so the main risks are under-dried material, humid storage and repeatedly opening a large container in a warm kitchen.
Shop With the Documentation
Whole material you can inspect yourself carries information a powder does not: Chaga chunks (100 g €25, 300 g €39) and dried shiitake (50 g €39, 100 g €69) can be seen and smelled before use. If you prefer capsules, Reishi capsules (120 caps €39) are single-species and sealed in portion sizes that limit storage exposure. Ask us for batch documentation before you buy — that question is one every supplier should be able to answer. Free shipping on orders over €50.
Related Articles
- Heavy Metals in Mushroom Supplements
- How to Read a Certificate of Analysis
- How to Store Mushroom Extracts and Powders
- What 10:1 and 8:1 Extract Ratios Actually Mean
- Mushroom Supplement Allergies
- How to Read a Mushroom Supplement Label
- How to Store Dried Amanita Muscaria Properly
Sources
- Zhao Z, Sun L, Liu J, et al. Occurrence and dietary risk assessment of Alternaria toxin in edible mushrooms: an application of a hydrophilic solid-phase microextraction fiber. Foods. 2026;15(11):1992. PubMed 42279778
- Toman J, Pickova D, Brandova K, Ostry V, Malir F. Investigation of ochratoxin A and citrinin occurrence in medicinal herbal products from the Czech market. Drug Saf. 2025;48(11):1215-1227. PubMed 40506653
- Kanabus J, Bryła M, Leśnowolska-Wnuczek K, Waśkiewicz A, Twarużek M. Mycotoxins occurrence in herbs, spices, dietary supplements, and their exposure assessment. Toxins (Basel). 2025;18(1):20. PubMed 41591166
- Tournas VH, Sapp C, Trucksess MW. Occurrence of aflatoxins in milk thistle herbal supplements. Food Addit Contam Part A. 2012;29(6):994-999. PubMed 22439650
- Windsor C, Kreynes AE, Chilton JS, Chioffi WA, Krishnamurthy A, Ishii M. Comparative study of chaga (Inonotus obliquus) dietary supplements using complementary analytical techniques. Int J Mol Sci. 2025;26(7):2970. PubMed 40243601