https://nutritionfacts.org/video/is-it-safe-to-eat-raw-mushrooms/
There is a toxin in plain white button mushrooms called agaritine, which may be carcinogenic. (Plain white button mushrooms grow up to be cremini mushrooms, and cremini mushrooms grow up to be portobello mushrooms—they’re all the exact same mushroom.
You can reduce the amount of agaritine in mushrooms through cooking. Frying, microwaving, boiling, or even just freezing and thawing lowers the levels. It is therefore recommended to cook mushrooms before consumption.
Boiling: The agaritine is reduced in the mushrooms but it transfers to the water (soup).
Frying for 5 to 10 minutes wipes out a lot, but microwaving is a more healthful way to cook, and
it works even better.
Just one minute in the microwave reduces the agaritine content of the [fresh sliced] mushrooms by 65 percent,” and only 30 seconds wipes out about half. So, microwaving is probably the easiest way to reduce agaritine levels in fresh mushrooms.
Dried mushrooms: If you put them into pasta water as there is about a 20-ish percent drop from the drying and the 60 percent-ish drop from boiling for 10 minutes and straining, more than 90 percent is wiped out.
According to a review paid for by the mushroom industry, we should not be worried.
“The available evidence to date suggests that agaritine from consumption of mushrooms pose no known toxicological risk to healthy humans.” The researchers acknowledge it’s considered a potential carcinogen in mice, but then you have to extrapolate that data to human health outcomes.
For example, the Swiss Institute of Technology estimated the average mushroom consumption in the country would be expected to cause about two cases of cancer per 100,000 people.
That’s actually similar to U.S. consumption, so one could theoretically expect about 20 cancer deaths per million lives from mushroom consumption. Now typically with a new chemical, pesticide, or food additive we’d like to see less than one in a million cancer risk. By this approach, “the average mushroom consumption ... would be 20-fold too high to be acceptable.”
To get it down to one in a million you could only eat about a half cup serving once every 250 days or something to remain under the quote-unquote “tolerable” limit. But to put that into
perspective, even if you were eating a single serving every single day, the resulting additional cancer risk would only be about 1 in 10,000. In other words, “if 10,000 people consumed a mushroom meal daily for 70 year[s], then in addition to the 3,000 cancer cases arising from other factors, one more case could be attributed to consuming mushrooms.”
But again, this is all based on the presumption that results in mouse models are valid in humans; this is all just extrapolating from mice. What we need is a huge prospective study to examine the association between mushroom consumption and cancer risk in people, but there weren’t any such studies... until now.
“Mushroom consumption and risk of ... cancer in [the] two large [Harvard] cohorts”, and... “no association between mushroom [intake] and [cancer]”.
Eating raw or undercooked shiitake mushrooms can cause something else, though: shiitake mushroom agellate dermatitis.
Flagellate as in flagellation, whipping, flogging. You break out in a rash that makes it look as if you’ve been whipped. It’s thought to be caused by a compound in shiitake mushrooms called lentinan, but because heat denatures it, it only seems to be a problem with raw or undercooked mushrooms.
Now it’s rare; only about 1 in 50 people are even susceptible. And it goes away on its own in a week or two. Interestingly, it can strike as many as ten days after you eat them, which is why people may not make the connection.
Sources:
Nordic Council of Ministers, Gry J, Andersson C, et al. Mushrooms Traded as Food. Nordic Council of Ministers; 2012.
Schulzová V, Hajslová J, Peroutka R, Gry J, Andersson HC. Influence of storage and household processing on the agaritine content of the cultivated Agaricus mushroom. Food Addit Contam. 2002;19(9):853-62.
Roupas P, Keogh J, Noakes M, Margetts C, Taylor P. Mushrooms and agaritine: a mini-review. J Funct Foods 2010;2:91-8.
Shephard SE, Gunz D, Schlatter C. Genotoxicity of agaritine in the lacI transgenic mouse mutation assay: evaluation of the health risk of mushroom consumption. Food Chem Toxicol. 1995;33(4):257-64.
Lucier G, Allshouse J, Lin BH. Factors affecting U.S. mushroom consumption. USDA. VGS 295-01. March 2003.
Lee DH, Yang M, Keum N, Giovannucci EL, Sun Q, Chavarro JE. Mushroom consumption and risk of total and site-specific cancer in two large u. S. Prospective cohorts. Cancer Prev Res (Phila). 2019;12(8):517-26.
Heer RS, Patel NB, Mandal AKJ, Lewis F, Missouris CG. Not a fungi to be with: Shiitake mushroom flagellate dermatitis. Am J Emerg Med. 2020;38(2):412.e1-412.e2.
Garg S, Cockayne SE. Shiitake dermatitis diagnosed after 16 years! Arch Dermatol. 2008;144(9):1241-2.
Watari T, Tokuda Y. Shiitake dermatitis. QJM. 2017;110(12):849.
Fang S, Bajoghli A, Bajoghli M. Shiitake mushroom-induced flagellate dermatitis. Ann Allergy Asthma Immunol. 2017;119(5):462-3.
Hamer S, Rabindranathnambi R. A wide-spread flagellate dermatitis. BMJ Case Rep. 2013;2013:bcr2012007682