Shiitake side effects: why you shouldn’t eat it raw
Short answer: The best-known side effect of shiitake is shiitake dermatitis: an itchy, streak-like skin rash after eating raw or insufficiently cooked shiitake. It goes away on its own, usually within a few days to a few weeks. In addition, gastrointestinal symptoms and an increase in eosinophils (a type of white blood cell) have been reported with daily use of shiitake powder, and you may be allergic to mushrooms.
Last updated: November 4, 2026 · Written by Florian Fermin
For most mushrooms, side effects mainly concern your stomach and medications. Shiitake is different: the main thing to pay attention to is how you prepare it.
Read our explainer article to learn what shiitake is and what it contains. Below, we cover only what is known about side effects and what that means for powder and capsules.
What are the side effects of shiitake?
The most frequently reported side effect is shiitake dermatitis after eating raw or partially cooked shiitake. Gastrointestinal symptoms, increased eosinophils in the blood, and allergic reactions have also been reported.
| Symptom | When was it reported? | What should you do? |
|---|---|---|
| Itchy, streak-like skin rash (shiitake dermatitis) | Mainly after raw or insufficiently cooked shiitake, once after taking shiitake tablets | Stop taking shiitake and contact your GP if in doubt |
| More eosinophils in the blood, sometimes with gastrointestinal symptoms | In 5 out of 10 healthy people who took 4 g of shiitake powder daily for 10 weeks | Stop if symptoms occur and report your shiitake use before a blood test |
| Allergic reaction | In people with a mushroom allergy, and in growers through contact with shiitake | Do not use shiitake. Stop immediately and call 112 if you have trouble breathing or swelling |
Can you eat shiitake raw?
No, you shouldn’t eat shiitake raw. Shiitake is an edible mushroom, but only when thoroughly cooked. The French food safety authority ANSES says this applies to fresh, dried, and powdered shiitake, and that briefly stir-frying it in a wok may not be enough (ANSES, 2021).
So you should skip shiitake in a salad, on carpaccio, or as a raw snack. In a French series of 59 cases, the rash appeared after eating raw or insufficiently cooked shiitake, including shiitake from a wok, in soup, and on pizza (Boels et al., 2022). So it’s not about the dish, but whether the shiitake is thoroughly cooked.
Not everyone reacts. In an earlier French case series, diners who ate cooked shiitake at the same meal had no symptoms, while those who ate it raw did (Boels et al., 2014).
What is shiitake dermatitis, and how can you recognize it?
Shiitake dermatitis is a skin reaction to eating raw or undercooked shiitake. You develop red, itchy streaks on your torso, arms, or legs, as if your skin had been struck by a whip. The suspected cause is lentinan, a beta-glucan in shiitake that breaks down when heated (Stephany et al., 2016).
- What it looks like: red, raised streaks, almost always itchy. In a systematic review of 50 cases, 98% had the typical streak-shaped rash and 78% had itching (Nguyen et al., 2017).
- When it starts: between 1 hour and 7 days after eating, with a median of 2 days (Boels et al., 2022).
- Sometimes more: in addition to skin symptoms, the review also mentions fever, diarrhea, and sores on the mucous membranes (Nguyen et al., 2017).
According to ANSES, French poison control centers have reported 11 to 15 cases each year since 2015. The actual number is probably higher because the rash is not always recognized and is sometimes mistaken for a reaction to sunlight.
How long does shiitake dermatitis last, and what can you do about it?
Shiitake dermatitis clears up on its own. In the French case series from 2014-2019, the rash lasted 1 to 40 days, with a median of 10 days, and everyone recovered fully. People who had eaten more shiitake had symptoms for longer (Boels et al., 2022).
If you develop this kind of rash after eating shiitake, stop eating shiitake and contact your doctor, especially if you have a fever or are unsure. Be sure to tell them you ate shiitake, as the rash is not widely known. In the French case series, 38 people were given medication for their symptoms, but there was no evidence that it sped up recovery.
If you eat raw or undercooked shiitake again afterward, the rash may return (ANSES, 2021).
Does this also apply to dried powder and capsules?
Almost all reported cases involve shiitake eaten raw or undercooked. Much less is known about powder and capsules. Here’s a summary of what the sources say.
- ANSES says shiitake must be cooked thoroughly, including when dried or powdered. ANSES does not mention capsules.
- One case in the Netherlands: a 31-year-old woman developed the typical linear rash three days after taking three tablets of a shiitake supplement (Reefman et al., 2013).
- One small study using powder: 10 healthy people took 4 g of shiitake powder every day for 10 weeks. In 5 of them, the number of eosinophils, a type of white blood cell, increased, and 2 of them also had gastrointestinal symptoms. These resolved after they stopped taking it (Levy et al., 1998).
- The same publication says that in an earlier study with shiitake, 17 of the 49 participants stopped because of a skin rash or abdominal symptoms.
None of these sources says whether drying breaks down lentinan. The frequency of shiitake dermatitis from powder or capsules has not been studied. To be honest, the 4 g per day in Levy’s study is as much as the maximum amount stated on our powder packaging.
If you want to be extra cautious, use the powder in a dish that’s cooked thoroughly. For instructions, see how to use shiitake powder. If you develop linear itching or a rash after consuming shiitake in any form, stop and contact your doctor.
Can you be allergic to shiitake?
Yes, as with other mushrooms, you can have an allergic reaction to shiitake. If you’re allergic to mushrooms or molds, don’t use shiitake, including as a supplement. Stop immediately. If you have difficulty breathing or swelling of your lips, tongue, or throat, call 112. If you have widespread itching, contact your doctor.
Contact dermatitis has also been reported among growers who handle shiitake mushrooms at work (Ueda et al., 1992). This is less relevant to normal use in the kitchen.
Who should consult a doctor before using shiitake?
Our packaging says: "Consult your doctor before use if you are pregnant, breastfeeding, taking medication, or have a medical condition." This applies to the supplement, including powder and capsules.
- Pregnancy or breastfeeding: We haven’t found any research on shiitake as a supplement during this period. Consult your doctor or midwife.
- Medications: the sources we reviewed do not mention any specific interactions between shiitake and medications, including the overview from Memorial Sloan Kettering (MSK, 2023). That does not mean they can be ruled out. So consult your family doctor or pharmacist.
- Blood tests: according to MSK, shiitake may increase the number of certain white blood cells. Having a blood test? Tell them that you use shiitake daily.
- Children: supplements are not intended for children.
How can you reduce the chance of side effects from shiitake?
You can reduce the chance of side effects by always cooking shiitake thoroughly, following the daily dosage on the packaging, and stopping as soon as you develop a rash or stomach symptoms.
- Follow the label. For the daily amount listed on our packaging, see shiitake supplement: capsules or powder, dosage and use.
- Choose a product with batch-specific lab tests. For how to read such a report, see how to read a mushroom supplement CoA.
Summary in 3 points
- The best-known side effect is shiitake dermatitis: an itchy, streaky rash after eating raw or undercooked shiitake, which goes away on its own.
- Little is known about the powder and capsules: there is one case after taking supplement tablets and one small study using 4 g of powder daily.
- Always cook shiitake thoroughly, follow the label, stop if you experience symptoms, and consult your doctor first if you are pregnant, breastfeeding, or taking medication.
Frequently asked questions
Is raw shiitake dangerous?
Not everyone reacts to it, but raw or undercooked shiitake can cause a severe, itchy rash in some people that can last from days to weeks. It goes away on its own. So always cook shiitake thoroughly.
Can shiitake capsules cause a skin rash?
One case has been reported after taking shiitake tablets. How often this occurs with capsules has not been studied. If you develop a rash, stop taking them and contact your family doctor.
Is shiitake safe during pregnancy?
No studies were found on shiitake as a supplement during pregnancy. Consult your family doctor or midwife.
Sources
- Stephany MP, Chung S, Handler MZ, Handler NS, Handler GA, Schwartz RA. Review article on skin reactions after eating shiitake. Am J Clin Dermatol. 2016;17(5):485-489. Europe PMC 27566177
- Boels D, Greillet C, Langrand J, Labadie M, Le Roux G, de Haro L, Bloch J, Sinno-Tellier S. Shiitake dermatitis reported to French poison control centers, 2014-2019. Clin Toxicol (Phila). 2022;60(8):954-959. Europe PMC 35404185
- Boels D, Landreau A, Bruneau C, Garnier R, Pulce C, Labadie M, de Haro L, Harry P. Shiitake dermatitis reported to French poison control centers, 2000-2013. Clin Toxicol (Phila). 2014;52(6):625-628. Europe PMC 24940644
- Nguyen AH, Gonzaga MI, Lim VM, Adler MJ, Mitkov MV, Cappel MA. Systematic review of the clinical features of shiitake dermatitis. Int J Dermatol. 2017;56(6):610-616. Europe PMC 28054338
- Reefman K, Galvis Martinez JC, Daelmans HEM. A woman with a linear skin rash. Ned Tijdschr Geneeskd. 2013;157(11):A5964. Europe PMC 23484519
- Levy AM, Kita H, Phillips SF, Schkade PA, Dyer PD, Gleich GJ, Dubravec VA. Eosinophilia and gastrointestinal symptoms after eating shiitake mushrooms. J Allergy Clin Immunol. 1998;101(5):613-620. Europe PMC 9600497
- Ueda A, Obama K, Aoyama K, Ueda T, Xu BH, Li Q, Huang J, Kitano T, Inaoka T. Allergic contact dermatitis in shiitake mushroom growers. Contact Dermatitis. 1992;26(4):228-233. Europe PMC 1395559
- ANSES and DGCCRF (2021). Notice on thoroughly cooking shiitake before consumption. April 9, 2021. anses.fr
- Memorial Sloan Kettering Cancer Center (MSK). About Herbs: Shiitake Mushroom. Updated February 14, 2023. mskcc.org
- Shiitake Powder and Shiitake Capsules packaging text (recommended use and warning), accessed November 4, 2026.
You can find all forms of our shiitake on the buy shiitake page.
This article is for informational purposes only and is not medical advice. Food supplements are not a substitute for a varied and balanced diet and a healthy lifestyle. If in doubt, during pregnancy, or when taking medication, consult your doctor or pharmacist.
