A Shiitake Mushroom Rash

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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.

Add a Comment25 Comments

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
Michele Blacksberg RN 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
Michele Blacksberg RN 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
EmpowHER Guest
Anonymous (reply to Michele Blacksberg RN)

Thank you both, I was told to take antihistamines by my doctor but will go back!! Thank you, again.

July 14, 2014 - 8:34pm
Leighandra Shenk (reply to Anonymous)

Sadly, you're probably just going to have to let it take its course. I suffered from this 2 years ago and I can remember how miserable I was like it was yesterday. Hot showers worked best for me. Good luck to ya!

July 14, 2014 - 6:34pm
EmpowHER Guest
Anonymous (reply to Leighandra Shenk)

Thank you. It just seems crazy that there isn't something that can be done to counteract it :( I've heard of it lasting up to 8 weeks!! How long until it cleared for you?

July 14, 2014 - 6:42pm
Leighandra Shenk (reply to Anonymous)

It was about 14 days. . .I won't even eat shitake mushrooms cooked! Never again.

July 14, 2014 - 6:56pm
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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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