Flagellate dermatitis from shiitakes

Shiitake-induced flagellate dermatitis in Mendocino County, California.


Something that seems to be worthy of a mention is observing a flagellate dermatitis (i.e. a scratch-like reaction that has also been described as “whiplash-like infiltrated erythemas“) that has occasionally resulted from someone eating raw or undercooked shiitake mushrooms.  This reaction was first reported in Japan by Nakamura in 1977 (see also Nakamura 1992).

Reports of isolated cases seem to be on the increase around the world. A friend had it happen to her.


flagellate rash following eating undercooked shiitakes

The rash is characterized by parallel raised red lines and urticarial erythemas can be present. It apparently typically clears up without any treatment after several days to a couple of weeks but can be itchy during the duration.

rash after eating undercooked shiitakes

rash on back of thigh after eating undercooked shiitakes

This post MIGHT be about the first report in Mendocino County of a flagellate dermatitis occurring following the consumption of undercooked or raw shiitake mushrooms. This type of rash usually occurs between 48-72 hours following ingestion (24-48 hr according to Ricar et al. 2012) and is believed to be a reaction to unheated or underheated lentinan according to many workers (examples: Díaz-Corpas et al 2011 & Poppe et al. 2012).  Lentinan, a polysaccharide, is considered to be one of the primary active compounds in shiitake.
Due to a lack of normal blood indicators or the typical symptomology accompanying allergic reactions (such as hives), this has been proposed to instead be a toxic response to inadequately heated lentinan. However lentinan is also known to induce “the production of the inflammation-promoting signal substance IL-1 and has a vasodilatative effect” and there is “increasing evidence that a genuine immunological sensitization in the sense of a T-cell-mediated late reaction could be involved” (Czarnecka et al. 2014).

Flagellate rash

Flagellate rash following undercooked shiitake consumption

The person to whom this occurred discovered that none of her doctors had the ability to correctly diagnose this; including a dermatologist. It cleared up within a couple of weeks as is the usual scenario. A visually disturbing internet search using her symptoms as search terms eventually lead to the right identification of the trouble.

Shiitake mushroom fruiting on a log

Shiitake mushroom fruiting on a log

References cited above:

Czarnecka A.B., B. Kreft & W.C. Marsch (2014) Postępy Dermatologii i Alergologii, 31 (3): 187–190. “Flagellate dermatitis after consumption of Shiitake mushrooms.”
Díaz-Corpas T., A. Mateu-Puchadesa, M.N. Coll-Puigservera & A. Marquina-Vila (2011) Actas Dermo-Sifiliográficas, 102: 830-832. “Flagellate Dermatitis After Eating Shiitake Mushrooms.”
Mak R.K. & S.H. Wakelin (2006) British Journal of Dermatology, 154: 800-801. “Shiitake dermatitis: the first case reported from a European country.”
Nakamura T. (1977) Japanese Journal of Clinical Dermatology, 31: 65-68. “Toxicoderma caused by shiitake (Lentinus edodes).”
Nakamura T. (1992) Contact Dermatitis, 27: 65–70. “Shiitake (Lentinus edodes) dermatitis.”
Poppe LM, D. Anders, H. Kneitz, E.B. Bröcker & S. Benoit (2012) Anais Brasileiros de Dermatologia, 87 (3):463-465. “Flagellate dermatitis caused by shiitake mushrooms.”
Ricar J., K. Pizinger & P. Cetkovka  (2012) The International Society of Dermatology,  letter to editor (2 pages).