4 Shiitake Mushroom Adverse Effects to Be Aware Of
By
Kathleen Ferraro
Updated on August 7, 2025
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Shiitake mushrooms are among the most popular types of mushrooms. They have a broad, brown cap with a thin, curved stem. Like other mushrooms, they’re rich in beneficial carbohydrates, vitamins, protein, plant compounds, and fiber. These nutritional benefits may help protect against high blood pressure, heart problems, and neurodegenerative diseases, among other benefits.
Shiitakes are generally safe to eat unless you have a known allergy or intolerance and as long as you buy them from the grocery store while avoiding wild varieties. But sometimes, shiitake mushrooms have side effects. Here are some of the potential pitfalls to munching on the mushroom.
1. Digestive Issues
The shiitake mushrooms you get from the supermarket are typically safe to eat. But wild-picked mushrooms can sometimes contain toxins that cause vomiting and diarrhea, according to Colorado State University.
Shiitake mushrooms are also hard to digest for people with an intolerance, which can occur when your body has difficulty processing a particular food. Food intolerance symptoms include:
- Gas
- Bloating
- Stomach pain
- Diarrhea
- Headaches and migraine attacks
- Heartburn
- Nausea
If you have an intolerance to this food, it's best to opt for a shiitake mushroom replacement in your meals (like other veggies) instead.
2. You Can Have a Mushroom Allergy or Intolerance
Though it's not one of the most common food allergens, it is possible to have a shiitake mushroom allergy or allergic reactions to other wild mushrooms.
An allergic reaction occurs when your immune system overreacts to a food:
- Hives
- Itchy skin
- A runny or blocked nose
- Itchy, teary eyes
- Swelling
- Wheezing
- Vomiting
- Diarrhea
- Stomach cramps
If you know you have a mushroom allergy, avoid eating shiitakes and any related products.
Some people can have a severe allergic reaction called anaphylaxis, which can make it difficult to breathe or lead to loss of consciousness, per the American Academy of Allergy, Asthma & Immunology. Call 911 immediately if you note the following symptoms after eating shiitake mushrooms:
- A tight throat, hoarse voice, or a lump in the throat
- Wheezing
- Chest tightness
- Breathlessness
- Tingling in the lips, scalp, hands, or feet
Are Mushrooms High in Histamine?
Mushrooms are low in histamines, according to research. Histamines are a type of amine, a chemical that can trigger intolerance reactions in some people. However, they do contain small amounts other amines (like putrescine), which is why dietitians sometimes exclude them for people following a low-histamine diet if they have a histamine intolerance. However, studies haven’t definitively linked putrescine to harmful effects in humans, although higher levels of putrescine than those in mushrooms have caused cell damage in test tube studies.
3. Shiitake Mushrooms Can Cause a Skin Rash
When it comes to shiitake mushroom side effects, a mushroom allergy rash isn't the only skin reaction you may experience. Indeed, eating the fungus raw or undercooked can also lead to a shiitake mushroom rash called shiitake flagellate dermatitis.
A shiitake rash typically develops a day or two after you eat the mushrooms, and shiitake dermatitis photos show that the rash looks like whiplash marks. A toxic reaction to lentinan, a substance in the mushroom causes it.
Shiitake mushroom dermatitis can be treated with antihistamine medicines or topical corticosteroids, and usually resolves with conservative management after around 10 to 14 days.
4. Shiitake Mushrooms Can Give You Food Poisoning
There aren't many documented outbreaks of food poisoning from mushrooms in the United States, according to Colorado State University.
Still, it's possible to get foodborne illness from bad shiitake mushrooms. This may be the case if you eat mushrooms that acquired bacteria during the growing or processing phase. Rotten mushrooms that have then entered the canning and distribution stage, which people eventually eat, have also caused food poisoning in the past.
Pathogens from raw meat, poultry, seafood, or eggs can also transfer onto mushrooms (or any other food, for that matter) if handled in close proximity.
Mushrooms are also perishable, according to the U.S. Food and Drug Administration (FDA). In other words, old mushrooms can make you sick if they haven't been properly stored.
So, what happens if you eat spoiled mushrooms? Food poisoning symptoms:
- Nausea
- Vomiting
- Watery or bloody diarrhea
- Abdominal pain and cramping
- Fever
To avoid foodborne illness, follow these tips:
- Clean your hands, utensils, surfaces, and food before preparing and eating a dish.
- Store and handle raw meat, poultry, seafood, and eggs separately.
- Thoroughly cook food.
- Promptly refrigerate perishable food.
What About Shiitake Mushroom Supplements?
Shiitake mushroom supplements and other mushroom extracts may actually support skin health. For instance, research suggests shiitake mushroom extracts may have antioxidant effects that have links to increased skin cell protection from certain environmental pollutants as well as potential anti-inflammatory activity. However, more research on humans is necessary to fully assess the skin benefits of shiitake extract.
It's best to check with your doctor before trying any of these products. That's because the FDA doesn't regulate supplements in the same way as medications, so there’s no guarantee that what you take is safe, contains the ingredients it says it does, or produces the effects it claims.
The Takeaway
- Shiitake mushrooms are nutritious but can cause digestive issues and trigger allergies. If you experience any severe reactions, seek medical attention immediately.
- Consuming raw or undercooked shiitake can cause a rash called shiitake flagellate dermatitis that involves a streaky, red rash.
- For those interested in supplements, it's vital to consult with a healthcare professional first, as current research on the skin benefits and safety of shiitake mushroom extracts remains limited.
- To avoid food poisoning from shiitake mushrooms, ensure you store them properly, follow safe food handling practices, and prioritize buying them from reliable sources over foraging.
EDITORIAL SOURCES
Everyday Health follows strict sourcing guidelines to ensure the accuracy of its content, outlined in our editorial policy. We use only trustworthy sources, including peer-reviewed studies, board-certified medical experts, patients with lived experience, and information from top institutions.
Resources
- Mushrooms. Colorado State University College of Health and Human Sciences.
- 7 Impressive Reasons to Eat Mushrooms. Cleveland Clinic. December 23, 2022.
- Mushrooms. Harvard T.H. Chan School of Public Health.
- Food Intolerance Versus Food Allergy. American Academy of Allergy, Asthma & Immunology. January 10, 2025.
- Food Intolerance. Cleveland Clinic. August 11, 2021.
- Food Allergy. American Academy of Allergy, Asthma & Immunology. May 15, 2025.
- Comas-Basté O et al. Histamine Intolerance: The Current State of the Art. Biomolecules. August 14, 2020.
- Histamine Intolerance. Allergy UK.
- Ma JY et al. Shiitake Flagellate Dermatitis. Mayo Clinic Proceedings. December 2022.
- Maruthappu T et al. A Characteristic Rash Caused by Shiitake Mushrooms – An Emerging Concern? Clinical Case Reports. May 5, 2021.
- Selecting and Serving Produce Safely. U.S. Food and Drug Administration. March 5, 2024.
- Mayo Clinic Staff. Food Poisoning (Foodborne Illness). Mayo Clinic. August 16, 2025.
- About Four Steps to Food Safety. Centers for Disease Control and Prevention. April 29, 2024.
- Paterska M et al. Macrofungal Extracts as a Source of Bioactive Compounds for Cosmetical Anti-Aging Therapy: A Comprehensive Review. Nutrients. August 22, 2024.
- FDA 101: Dietary Supplements. U.S. Food and Drug Administration. June 2, 2022.
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Lynn Grieger, RDN, CDCES
Medical Reviewer
Lynn Grieger is a registered dietitian-nutritionist, certified diabetes care and education specialist, certified personal trainer, and certified health and wellness coach. She completed requirements to become a registered dietitian at Valparaiso University in 1987 and completed a dietetic internship at Ingalls Memorial Hospital in Harvey, Illinois, in 1988.
Lynn brings her expertise in nutrition, exercise, and behavior change to her work in helping people reach their individual health and fitness goals. In addition to writing for Everyday Health, she has also written for websites and publications like Food and Health Communications, Today's Dietitian, iVillage.com, and Rodale Press. She has a passion for healthy, nutrient-dense, great-tasting food and for being outdoors as much as possible — she can often be found running or hiking, and has completed a marathon in every state.