Shiitake mushrooms must be cooked thoroughly before eating


One night, Eglė Janušonytė, the doctor on duty in the emergency department of the University Hospital of Geneva in Switzerland, saw an elderly man who said that his skin was so itchy that he could not sleep at all. Janušonytė was completely stunned when he looked at the 72-year-old's back and upper buttocks with suspicion, a picture that "once you see it, you won't forget" – covered with dense red marks, as if the old man had been brutally assaulted and beaten mercilessly. However, Janušonytė did not forget that the old man said that it was particularly itchy.

Before coming to the hospital, the old man had been in such a strange itching situation for 2 days. He had taken a number of allergy medications, including antihistamines and prednisone, but they had no effect. Janušony and a colleague judged that the elderly man had a rare form of dermatitis: flagellate erythema, based on the red marks on his back. In a recent study published in the New England Journal of Medicine (NEJM), they told the story of the case.

In order to find the specific cause of the disease, they searched for possible situations one by one. They found that although the elderly man had erythema, there was no swollen lymph nodes, which ruled out viral and bacterial infections. In addition, the patient is not classified as dermographism (usually related to infection, depressed mood, and medications) or mucosal involvement. Eventually, they focused on two possible causes, one being taking bleomycin and the other being raw or undercooked shiitake mushrooms.

I guess you can guess what the reason is. As Janušony learned more about the eating habits of the elderly, they found that more people began to try this tender and chewy ingredient as shiitake mushrooms, a delicious mushroom native to Asia, became the second most produced mushroom in the world and spread to Europe. And just 2 days ago, the old man was trying to make a new dish, which happened to have shiitake mushrooms. He is believed to have eaten underripe shiitake mushrooms and developed whip erythema induced by shiitake mushrooms – also known as shiitake dermatitis

Not only in Switzerland, but in a study published in Clinical Toxicology in 2014, French scientists collected cases of shiitake dermatitis that had occurred in the country for more than 10 years and found that 15 of the 32 patients had a rare form of shiitake dermatitis throughout the body due to direct consumption of raw shiitake mushrooms. And those who don't like the taste of raw shiitake mushrooms are lucky enough to avoid this. In addition, related cases have been reported in Germany, Brazil and other countries. Since shiitake mushrooms are native to East Asia, this condition is more common in Asian countries, and the earliest cases of shiitake dermatitis were reported by Japanese scientists in 1974.

Why is the small shiitake mushroom so powerful? It has to do with Lentinan, a polysaccharide in the cell wall of the fruiting body cells of shiitake mushrooms. This substance is not heat-tolerant, and when cooked (the way most people eat it), this key substance that causes shiitake dermatitis is destroyed. However, if a person eats raw shiitake mushrooms without cooking or directly, the mushroom polysaccharides enter the human body for about 24 hours, which may cause the eater to develop erythema all over the body, striped itch rash, not only on the back and limbs, but also on the face and back of the head. These erythema can cause an extremely itchy sensation that can be further exacerbated by exposure to sunlight.

Fortunately, doctors have found that shiitake dermatitis is a self-limiting disease, in other words, although there is no corresponding drug to treat this disease, the symptoms caused by it will gradually disappear after 3~21 days. For the old man who lived in Geneva, Janušony and his colleagues prescribed him some glucocorticoids and oral antihistamines to relieve his symptoms. At a follow-up visit after 2 weeks, they found that the itching symptoms had subsided, although there were still some spots on the body. However, as mentioned above, these drugs have no obvious effect, and it can be expected that the elderly will still be very itchy and uncomfortable in the process of recovering from the condition, but they have to endure it.

Researchers have been able to explain why lentinan dermatitis is caused by lentinan polysaccharides, which promote the secretion of interleukin-1 and other inflammatory cytokines by immune cells, a process that causes vasodilation, bleeding and rashes. Miraculously, however, in addition to the uncomfortable symptoms of whip erythema, the shiitake mushroom, which is a Chinese and Japanese folk medicine, can also be used as an anti-cancer chemotherapy drug.

Lentinan has multiple sugar chains and a very special structure, which also gives it a wide range of anti-tumor and anti-cancer activities. It mainly regulates interleukins (IL), macrophages, helper T cells and natural killer cells (NK) to improve the efficacy of chemotherapy and radiotherapy for cancer and improve the quality of life of patients during treatment.

Different people have different sensitivities to lentinan mushrooms, which leads to different degrees of immune response triggered by lentinan in them, which determines whether they develop lentinan dermatitis. For example, in a clinical trial, 9 out of 500 cancer patients who received lentinan injections developed lentinan dermatitis. However, as long as the intake of lentinan is no longer consumed, lentinan dermatitis can be improved. For those who need to treat cancer, other treatments may be tried. However, if the structure of lentinan polysaccharides can be properly modified to avoid the appearance of lentinan dermatitis, it may be better to help cancer patients.

However, if there are whip-like erythema on the body, or a large area of erythema, but it is not related to eating shiitake mushrooms raw, then you need to focus on some other factors. According to a paper published last year in Mayo clinic proceedings, a 23-year-old male patient received chemotherapy with a combination of three anticancer drugs, including bleomycin, for external germ cell tumors. Within 4 days, he developed pimples on his trunk, neck, scalp, hands, and limbs, which then developed into extremely itchy whiplash erythema.

The treating doctor also prescribed him some antihistamines, as well as topical and oral corticosteroid medications. However, the whip erythema becomes more severe because the patient needs to continue chemotherapy -- with bleomycin. According to some studies, 8%~20% of patients treated with bleomycin may develop whiplash erythema, and this situation has nothing to do with the route of administration and dose.

There are some differences in whiplash erythema caused by bleomycin and lentinan mushrooms. Some studies have shown that bleomycin causes a toxic reaction in human skin. When there are not enough corresponding hydrolytic enzymes in the body to remove bleomycin, it can be deposited in skin cells, damaging keratinocytes and melanocytes. When these cells are destroyed, pigment deposits on the surface of the skin, creating linear, whip-like erythematous patches or papules. This condition can also resolve on its own, but in severe cases, it is still necessary to stop using the causative drug promptly. In addition to shiitake mushrooms and bleomycin, whiplash-like rashes may also be associated with adult Still's disease (AOSD), dermatomyositis, infection with the human immunodeficiency virus (HIV), and taking some other medications.

If you experience similar symptoms, be sure to see your doctor promptly. In addition, shiitake mushrooms must be cooked thoroughly before eating.