Health Alert Shiitake Mushrooms should be well cooked

Alerte santé Les champignons Shiitake (lentin) doivent être bien cuits

If you have cooked shiitake mushroom (Lentinula edodes) you will know that one of its prized attributes is not shrinking as much as button and brown mushrooms (Agaricus bisporus) even with heavy stewing. When dried the shitake acquires another aroma, much appreciated, particularly in Chinese and Japanese cuisine. Asians enjoy the shiitake not only for its culinary versatility but also for its many claimed medicinal properties such as enhancing immunity, lowering blood cholesterol, controlling diabetes and prophylaxis against cancer. Except for lowering cholesterol through its eritadenine content, none of these effects is well validated.

Although the mushroom is edible, it produces a severe skin reaction in a few individuals, particularly when eaten raw or undercooked. The aim of this post is to alert consumers to this rare but alarming adverse cutaneous reaction (see Photos) first reported in Japan in 1977. As the Western diet is increasingly cosmopolitan and as cultured shiitake becomes readily available in supermarkets, cases of this adverse effect will become more common but may escape the attention of both doctors and consumers leading to misdiagnosis and inappropriate treatment. A communication is a medical journal reported on a case that had been missed for sixteen years.

Points to note:

1.The alarming itchy eruption can appear on any part of the body but often on the back in the form of whiplashes; hence the term ‘flagellate’ or ‘linear’ for describing its appearance.

2.There may be a delay of up to several days from consumption to appearance of the itchy rash. A report describes the reaction in a returning traveller exposed to the mushroom overseas.The rash may persist for several days. Hence the first medical consulation may well not be until days after exposure.

3.Cooking reduces the risk of having the reaction because the likely offending polysaccharide, lentinan, is heat labile.

4.If you develop the rash, do not panic. It will resolve with moisturisers and if necessary your doctor can prescribe some steroid cream to soothe the itch. Hydrocortisone cream can be obtained over-the-counter in many countries.

5.There are other causes of similar rashes, including some antibiotics and anticancer drugs (e.g. belomycin and trastuzumab). So, differential diagnosis is important through careful history taking. If the rash does not improve within a couple of days or appears infected, seek medical help.

6.The may well be a genetic predisposition to the rare reaction although the exact mechanism has yet to be unravelled. So, a family-history of the dermatitis may well suggest further caution.

7. Enjoy the shiitake but cook it well first. Do not add it raw to your salads.

8.Some mushroom contain statins, the widely used cholesterol-loweing agents. If treatment is deemed necessary the licensed products are better as they allow accurate dosing. The shiitake contains eritadenine, also a cholesterol-lowering agent but its properties are less well defined than those of statins. So it is best to stick to the statins if required as their risk-benefit profiles are well defined.

9.Please see our previous post on the oyster mushroom which contains the statin drug lovastatin.

Further reading:

Nakamura T. Shiitake (Lentinus edodes) dermatitis. Contact Dermatitis 1992;27:65-70.

Garg S, Cockayne SE. Shiitake Dermatitis Diagnosed After 16 Years! Archives of Dermatology 2008;144:1241-2.

Hérault M, Waton J, Bursztejn AC, Schmutz JL, Barbaud A. La shiitake dermatitis (dermatose toxique au lentin) est arrivée en France. Annales de dermatologie et de venereologie 2010;137:290-3.

Mills H, Walker SL. Shiitake Mushroom Dermatitis in a Returning Traveler. Am J Trop Med Hyg 2020;102:483.

Mumford B, Chong A. A rash of poor cooking. Australian Journal for General Practitioners 2022;51:143-4.

Janušonytė E, Pünchera J. Shiitake Dermatitis. N Engl J Med 2023;389:1415.

Boels D, Landreau A, Bruneau C, et al. Shiitake dermatitis recorded by French Poison Control Centers – new case series with clinical observations. Clinical Toxicology 2014;52:625-8.

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Photo Credits – Mills et al., 2020 and ALWP CEBP