Shiitake Flagellate Dermatitis

What is Shiitake Flagellate Dermatitis?

Shiitake dermatitis is a unique rash that can develop after consuming raw or undercooked shiitake mushrooms. It is distinguished by pruritic, erythematous, linear streaks that mimic whiplash marks, hence the name flagellate. It can be referred to as flagellate erythema or toxicodermia.
Shiitake mushrooms are consumed most frequently in China and Japan, and shiitake dermatitis is most common there. It affects approximately 2% of people who eat mushrooms raw or lightly cooked. It has been documented in people of all ages, with men being greater than women.

Causes of Shiitake Flagellate Dermatitis

Shiitake flagellate dermatitis is a toxic reaction to lentinan, which is contained in fresh, powdered, and lightly cooked shiitake mushrooms. Lentinan is a thermolabile polysaccharide that stimulates interleukin-1 secretion, resulting in vasodilation, hemorrhage, and rash. It is not caused by skin contact with the mushrooms.

Clinical features of Shiitake Flagellate Dermatitis

Shiitake dermatitis is characterized by a flagellate rash that typically develops 24 hours after consuming raw or undercooked mushrooms. The symptoms can appear within a few hours or up to 5 days after consuming the mushrooms. Linear streaks of itchy erythematous papules and, occasionally, petechiae appear.There may be localized swelling. It primarily affects the trunk, but it can also affect the limbs, neck, or head. It has no effect on mucousal surfaces.The rash can worsen with sun exposure.

Some people with shiitake flagellate dermatitis experience additional symptoms:

  • Localized oedema.
  • Malaise
  •  Fever
  • Lip tingling
  • discomfort when swallowing
  • Diarrhoea
  • Tingling in the hands and feet

Diagnosis of Shiitake Flagellate Dermatitis

The diagnosis is clinical, based on the typical history of recent mushroom consumption and the development of the rash. There were no specific laboratory findings. Usual tests may include:

  • Full blood count
  • Liver function tests.
  • Urea and electrolytes

Histopathology is nonspecific with hyperkeratosis, spongiosis, dermal oedema, and a perivascular lymphocytic infiltrate containing eosinophils.

Treatment of Shiitake Flagellate Dermatitis

Shiitake flagellate dermatitis is self-limiting. It is unclear whether therapy accelerates the rash’s remission.

  • Oral antihistamines
  • Topical corticosteroids

As the rash heals, those who are affected should avoid exposing their skin to the sun.

There is usually an improvement after two days and a complete resolution after three weeks.

Prevent future attacks by thoroughly cooking shiitake mushrooms before eating.



Written by:

Atheer Alhuthaili, Medical Student.

Revised by:

Maee Barakeh, Medical Student.