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A Shiitake Mushroom Rash

By HERWriter
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Food Allergies related image Photo: Getty Images

Shiitake mushrooms are an Asian delicacy frequently added to stir-fries or used as a source of protein in vegetarian cooking. What may come as is surprise is that one can be “allergic” to undercooked shiitake mushrooms so it is suggested that people always cook them thoroughly before eating.

On February 18, 2011, the New York Times ran an article about a woman who developed a pretty severe red-lined rash all over her body. The rash was not particularly itchy nor was it painful. Her doctor was stumped so he called in other doctors to evaluate her. After examining the rash, one of the doctors paused for a moment then asked her if she had recently had shiitake mushrooms? Surprised, she said she had a few days before the outbreak as a sample sautéed in garlic and oil at a grocery store.

Apparently, the shiitake mushrooms were undercooked which left a starch-like substance in the mushrooms called lentinan that was not sufficiently broken down in the portion she ate. Heating lentinan prevents the body from having a toxic reaction to it when consumed. Unlike a true allergy, people who react to uncooked shiitake mushroom do not show a typical immune response in their blood levels nor do they develop classic symptoms of hives, itching and swelling. The response to shiitake mushrooms has been labeled as a toxic reaction rather than an actual allergy.

Interestingly, lentinan has been used as an anti-cancer agent. According to sloankettering.org, lentinan use has been studied extensively. The protein component of lentinan is called lentin, which has been found to have anti-fungal properties, reduce the growth of leukemia cells and suppress HIV viral enzyme activity. Lentinan has also been studied for use in prostate cancer suppression though the results did not show it alone could sufficiently prevent it. It is important to note that most clinical studies do not test patients using actual shiitake mushrooms but use extracts in powder form.

Shiitake mushroom do have natural health and nutritional benefits but they should never be eaten raw even if in the past one has not had any problems. Allergic or toxic reactions can occur even after years of exposure to a substance then without warning, the body can react even though the substance had never caused an outbreak before. Additionally, all mushrooms contain other molds and spores that could cause an actual allergic reaction so it is best to have a doctor evaluate any rash that occurs after consuming mushrooms.


Michele is an R.N. freelance writer with a special interest in woman’s health care and quality of care issues. Other articles by Michele are at www.helium.com/users/487540/show_articles

Add a Comment29 Comments

EmpowHER Guest

About a year or so ago I ate some raw shiitake mushrooms as I was preparing a noodle soup, then I just cooked the rest lightly in the broth. 2-3 days later I was raw with striated lashes all over my legs, torso, back and a hideous itchy rash everywhere, yes everywhere! It was almost reaching my eyes, which can be dangerous and can impair vision. I went to A&E immediately as it started to crawl,up my arms from my fingers etc... They gave me steroids tablets to take and there is a topical antihistamine you can get in tablet form from Boots etc.. Which does work well to reduce the itch. Other ones do not have an effect because it is a reaction of the skin. It is a sit and wait it out situation. Mine lasted for 10 days which was unbearable! I have not eaten even a regular mushroom since! And I have not missed them either.
Good luck to all, I feel your pain!

June 20, 2016 - 10:38am
EmpowHER Guest

Hey, a year ago i experienced a very itchy rash after eating a shitake mushroom. it lasted 2 weeks and since than i haven't touched a shitake mushroom.
i understand that you have to cook it properly, but is it some of a guarntee that i won't experience those symptoms?

June 18, 2016 - 7:28pm
EmpowHER Guest

I am currently experiencing this rash now. Today is the second day with it. Yesterday was horrid. Hives, welts and blisters EVERYWHERE. Doctor recommended antihistamines - which of course don't work (its not an allergic reaction). But Doc also recommended Mylanta antacid as a topical treatment. Oh the relief it is awesome - who would have thought you could use Mylanta this way. Much better than calamine lotion. Try it.

January 30, 2016 - 9:16pm
EmpowHER Guest

I am going through an outbreak now. I had an asian dish of curry on Monday 12/21/2015 at work, went through a lunch line, picked fresh veggies that included shiitake mushrooms, picked my protein and it was cooked in front of me for a short time then topped with curry sauce. The meal was great and loved the mushrooms but they didn't love me back. I had no clue what it was until I google searched slash rash and up popped all this info on Shiitake Mushroom reaction and the images matched mine perfectly. I have been taking benedryl (2 every 4 hours) which help with the itching and covering all my blisters with lamisil. Yes, the foot fungus cream. I figured the mushroom was a fungus and the blistery rash was similar to a foot fungus so that is what I chose. It helps greatly. I went a day without taking the meds and putting on the cream and I suffered. I still have some itching but without the cream it was like having hundreds of fire ants on my hands. It will get better and then you will see new stuff appear but for the most part it has to take its course. I hate taking meds, especially steroid type meds so I opted not to see a doc and self treat (no fever, airways were open and no danger of infecting my eyes that I could see) Had any one of these occured I would have got myself to the doc. It has worked for me. I know others can have a more serious reaction that will close up your airway... SEE YOUR DOC If your airways are good and you just look like you got a whip lashing and blistery rash, this has worked well for me. I have avoided scratching to the best of my ability and everything is drying up and going away. I am on my 6th day, no more blisters at least, which were ALL over my hands, face, lips, head, private areas, legs and arms, basically everywhere. Still have the slash looking rash on my bum and legs but the ones on my sides have gone away with remnants of the outbreak, little red specks everywhere. I hope this helps someone as I didn't have a clue how to treat or if I was contagious or not. Which I wasn't. Happy shiitake dermatitis to you!!

December 29, 2015 - 10:40am
EmpowHER Guest

I also got the red rash after eating Shitake mushrooms. Went to the Dr, he prescribed Panafcortelone (Prednisolene 25mg). The Dr advised that where the rashes are long red lines, they are caused by scratching during my sleep (see Dermographia), otherwise it comes out in small red lumps, some with watery centres. They lumps are in my scalp, forehead, arms, hands (palms and forehand), upper/lower legs and anus. The same small lumps are also in my mouth, along the gums and on rear roof of my mouth. The Panafcortelone seems to have eased the symptoms and I am only 5 hours into the first course. I hopes this helps others out who seem to be having problems finding a solution. I ate some raw Shitakes after soaking. Will ensure I soak and cook thoroughly (boil the hell out of them) next time and cut off the stems prior to cooking.

January 7, 2015 - 11:36pm
EmpowHER Guest

Thanks Michele - I'm a male 53 yrs in the UK - I ate some raw shiitake whilst making a mushroom omelette (Sunday) and began to react after 24 hours - rash on neck,face, hands - Wednesday went to GP (family physician) and given oral prednisone 28 tabs of 5mg - 30mg OD until all tabs used up - The rash is composed of raised red papules that are arranged in lines like scratch marks. I also had a reaction in my mouth - Dr said get to emergency room (a and e) if I was struggling with breathing . I'll probably avoid shiitake once this settles . I think this is pretty unusual in the UK so Dr couldn't be too sure - anyhow hope this doesn't last too long - Tim

August 14, 2014 - 2:48am
HERWriter (reply to Anonymous)

Glad you received medical attention early.  Hopefully the short run of steroids will help. 


take care,


August 14, 2014 - 4:59am
EmpowHER Guest

I'm an Australian who ate almost half a cup of raw shiitakes. I have come down with shiitake dermatitis and it is everywhere! Hair, neck, back, stomach, buttocks, groin area, legs, arms - no-where has been spared! Antihistamines simply do not work! One week later and it seems to be spreading rather than getting better! I am going to get some Calamine lotion after reading one readers post but doctors seem to have no idea how to treat this and there is little literature about it.

July 14, 2014 - 6:09pm
HERWriter (reply to Anonymous)

I don't know how you can find someone who knows more.  It sounds like you might need a short run of oral steroids if it is getting worse. 

Is there an allergist you can make an appointment with? That would be the type of doctor experienced with these kind of reactions.

Hope it settles down soon.


July 14, 2014 - 7:32pm
EmpowHER Guest
Anonymous (reply to Michele Blacksberg RN)

Apparently, this is NOT an allergic rash per se, but a toxic reaction to a protein, so cortisone and benadryl are not very helpful. Literature suggests that it usually clears up in two weeks. As always, be on watch for severe type symptoms, i.e. difficulty breathing, irregular heart beat/rate, etc. but these are unlikely. Also, scabies will show up with a very similar rash. Best to see a dermatologist for an accurate dx.

Kevin C. RN

January 22, 2015 - 4:49pm
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We value and respect our HERWriters' experiences, but everyone is different. Many of our writers are speaking from personal experience, and what's worked for them may not work for you. Their articles are not a substitute for medical advice, although we hope you can gain knowledge from their insight.

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