Food Allergies

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Maryann Gromisch RN Guide

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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, 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.

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.

Add a Comment13 Comments

EmpowHER Guest

Thank you! Finally an answer! The itchy scalp is driving me crazy! I plan to go back to the doctor and show her what I found. It doesn't sound as if there is any relief for this, other than to ride it out. I'm 7 days into this and the scratch-like rashes seem to be getting better.

December 14, 2013 - 10:12am
EmpowHER Guest

Thank you so much! I started having all these symtoms 2 days ago, that was 2 days after eatinggabout 5 or 6 slices of shiitake mushrooms (so it took very little to have this reaction). Itching and red rash are almost everywhere on my body. It iches a lot and i even have some marks in my face. I was given antihistamine but they don't work... I don't want to endure this for weeks :( oh well. Can't wait to return to normal!

December 5, 2013 - 12:18pm
EmpowHER Guest

No itch? Total BS. I am itching like crazy all over and yes, Shitake is the culprit. Itch is worse in scalp.

January 23, 2013 - 4:03pm
EmpowHER Guest
Anonymous (reply to Anonymous)

My husband has the rash over his entire body. Very ichy and burns. He can't find any relief and hasn't slept in days. Any suggestions to help with the iching and burning?

January 29, 2013 - 9:05am
Michele Blacksberg RN HERWriter

You are welcome!

I've got to say, I wrote this article almost a year and a half ago and every so often, someone comes across it and is thrilled to find out what may be causing their rash. Glad to be of help!  

August 12, 2012 - 7:44pm
EmpowHER Guest

Wow. I'm sorry for everyone's discomfort but so glad to know its not just me! This is my 2nd bout with this rash in 4 weeks, the first time I thought it was just a heat rash. But in both instances, I had been eating raw shiitake mushrooms for about 2 days prior. Why aren't there more warnings about this in the media or even a sign at the grocery store? I am covered hairline to feet (and worse of all in my pubic region!) in red welts, streaks, bumps, and flat red dots that look like petechiae. I took a steroid last time but I still endured it for about 7 days. Thanks for the info, Ms. Blacksberg!

August 12, 2012 - 5:50am
EmpowHER Guest

Sooooo very glad I found this! I am suffering my 10th day of itchiness. I know the woman in the article didn't experience the itch, but I think my immune system kicked in causing an allergic reaction as well. My right eye was swollen! I had the streaks and red bumps all over. The rash is fading now. I ate raw shiitake mushrooms two days in a row and got the rash on the 3rd day. It started on my forearms, my eye, and my neck. The welts on my torso and back showed up the next day. I also had welts on my shoulders, behind my ears, my face, hairline, and one down my nose. I don't have health insurance so I haven't seen a doctor. Antihistamines helped somewhat with the itching. A hot shower provided the most relief. I hope this itching goes away soon. Not at all intense, but annoying nontheless.

April 20, 2012 - 6:54pm
EmpowHER Guest

I have a rash covering almost every inch of my body. The only new food consumed was raw shiitake mushrooms-eaten in salads over several days. Small red dots and lines everywhere with large red patches on my neck, middle back, and hips. Have had the rash for five days, with new areas of dots still breaking out, mostly on my legs. Was given a prescription for prednisone for 10 days, 39 pills, but this is serious medicine, so I am toughing it out using Sarna anti-itch lotion with menthol. Most comfortable with nothing on in cool air!

August 6, 2011 - 11:44am
EmpowHER Guest
Anonymous (reply to Anonymous)

I have the same rash all over my body due to eating two mushrooms. It has been 4 days of painfull itching rash all over body. I was also prescribed prednisone but thought i could wait it out but still no reduction. Anyone have an idea of how long this rash typically lasts?

March 11, 2012 - 12:48am
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