Shiitake Mushroom Dermatitis: A Case Report

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Megan Litzau, MD
Emergency Medicine Resident
Indiana University
AAEM/RSA Social Media Committee

A 31-year-old African American male presented with an erythematous rash of 8 days duration. The patient had been seen in the emergency department one week prior for the rash. At that time, he was given Eucerin cream, prednisone taper, and diphenhydramine. The patient returned one week later as the rash had not improved. Upon examination, the patient had a violaceous, linear rash across his torso and all of his extremities. The linear lesions appeared as though the patient had been scratching. However, he adamantly denied scratching and was unable to reach several of the lesions on examination. Upon further questioning, the only recent change in the patient’s habits was consuming a large amount of uncooked shiitake mushrooms 9 days prior. Approximately 12 hours after consuming the mushrooms, the rash appeared. Since that time, the rash had persisted. The rash was initially erythematous and had faded to a violaceous color during the course of the rash. The patient noted the rash to be constantly pruritic, which prompted his return visit to the emergency department. The patient also noticed that the rash and itching got worse when he was working outdoors. 

Diagnosis: This patient was diagnosed with Shiitake mushroom dermatitis.

Management: On his return visit, the patient’s report of shiitake mushroom ingestion was investigated further. The Indiana Poison Center was consulted at that time. After consultation, the patient was again placed on prednisone and treated with diphenhydramine. The diagnosis was discussed with the patient along with the expected course according to the case report literature that existed on the topic. The patient was discharged from the emergency department and was lost to follow-up.

Discussion: Shiitake mushrooms are edible mushrooms that can be found in stores in the United States. Eating uncooked shiitake mushrooms has resulted in some patients developing dermatitis. This dermatitis can occur within 12 hours to 5 days (average 24 hours) and may persist for 3 to 21 days.[1] The rash tends to consist of linear, pruritic urticarial lesions. Of note, there were some other case reports regarding photosensitivity of the rash in which increased skin irritation was noted.[1] The literature that was previously available regarding shiitake mushroom dermatitis is limited to case reports and case series that are primarily found in the European literature.

While there is no validated treatment for these patients, the literature discusses the use of antihistamines and steroids. There has been documented use of both oral and topical steroids; however, there has been no comparison undertaken to determine if either is superior. The steroid of choice, dosing, and duration of treatment has also not been defined in the literature.

As with any dermatitis, there is always the concern for secondary infection. Therefore, it is important to discharge the patient with return precautions for possible secondary infection.

To date, the exact mechanism of action of the shiitake mushroom dermatitis is unknown. Skin biopsies that have been done on this rash have been nonspecific.[2] The reported cases in the literature have resolved. As there are an increasing number of health food stores in the United States, awareness of Shiitake mushroom dermatitis may prove useful as it produces an impressive rash that is pruritic, but is self-resolving.


1. Boels D, Landreau A, Bruneau C, et al. Shiitake dermatitis recorded by French Poison Control Centers – new case series with clinical observations. Clin Toxicol (Phila). 2014;52(6):625-8.

2. Wang AS, Barr KL, Jagdeo J. Shiitake mushroom-induced flagellate erythema: A striking case and review of the literature. Dermatol Online J. 2013;19(4):5.