Food Poisoning from Mushrooms: Symptoms and Timing

Food poisoning from mushrooms comes from two different causes, and they need different responses.

• A poisonous mushroom. Usually a wild mushroom picked by mistake, or a poisonous one mixed in with market mushrooms. Hong Kong's Centre for Food Safety notes that mushroom toxins are produced by the fungi themselves and most cannot be made harmless by cooking, canning or freezing. This is the dangerous kind.
• An edible mushroom gone wrong. Contaminated with bacteria such as Listeria, spoiled in storage, or eaten raw or undercooked. Health Canada lists contaminated compost and water, animals, unsanitary handling, cross-contamination from raw meat and poor storage as routes for bacteria.

The Centre for Food Safety also lists a middle case: some edible mushrooms eaten raw or undercooked contain heat-sensitive gut irritants, naming the ZhuDu mushroom (Clitocybe geotropa), the button mushroom and the straw mushroom.

Hong Kong's Centre for Food Safety describes mushroom poisoning as usually acute, with symptoms depending on the species and the amount eaten:

• Most common: nausea, vomiting and abdominal pain.
• With some species: extreme thirst, profuse sweating, hallucinations, coma and other neurological symptoms.
• Allergic-type reactions: self-limiting stomach upset in some sensitive people after common edible mushrooms.
• With alcohol: stomach and heart symptoms if alcohol is drunk within 72 hours of eating the fat-foot funnel cap (Clitocybe clavipes) or the common ink cap.
• Severe cases: liver failure and death.

Bacterial food poisoning looks different. For Listeria, the CDC describes diarrhoea and vomiting in the gut form, and fever, muscle aches, headache, stiff neck, confusion, loss of balance and seizures in the invasive form; in pregnancy it can cause miscarriage, stillbirth or premature delivery.

Timing is the most useful clue, because it points to the kind of toxin. Wikipedia's rule of thumb: symptoms within about 6 hours usually mean gastrointestinal irritants that rarely cause lasting damage; symptoms that start 6 to 12 hours or more later can mean potentially fatal toxins.

• Raw or undercooked morels: in a 2023 restaurant outbreak in Bozeman, Montana, symptoms began a median of 1 hour after the meal; 51 people fell ill, 3 were hospitalised and 2 died (CDC MMWR, 14 March 2024).
• Fly agaric (ibotenic acid): 30 minutes to 2 hours (Wikipedia).
• Ink caps with alcohol: 5 to 10 minutes after the drink (Wikipedia).
• False morels (gyromitrin): usually 6 to 12 hours, sometimes as early as 2 hours (Wikipedia).
• Death cap and other amatoxin mushrooms: 6 to 12 hours with no symptoms, then gut symptoms, then liver damage from around day two (Wikipedia).
• Webcaps (orellanine): 3 to 20 days, with kidney failure (Wikipedia).
• Listeria: gut illness within 24 hours; invasive illness usually within 2 weeks (CDC). In the 2016 to 2019 US enoki outbreak, most people fell ill 1 to 4 weeks after eating, with a range from the same day to 70 days.

Do not wait for symptoms to decide. Poison Control warns that symptoms from poisonous mushrooms can be delayed for many hours.

Usually nausea, vomiting, abdominal pain and diarrhoea (Centre for Food Safety, Hong Kong). The danger is that the deadliest mushrooms give no first sign for hours: death cap poisoning is silent for 6 to 12 hours, and after the gut phase a person can feel fine for up to 72 hours while the liver is being damaged (Wikipedia). If a wild mushroom was eaten, the eating itself is the signal to call.

Spoiled or contaminated edible mushrooms cause bacterial food poisoning rather than mushroom toxin poisoning. What the sources warn about:

• Signs of spoilage. The Centre for Food Safety advises against buying mushrooms with coloured spots, an abnormal smell or slime, or with growing medium left on them, and says to discard soaked dried mushrooms that turn slimy or smell abnormal.
• Soaking dried mushrooms. Soaking promotes bacterial growth; keep it to about 2 hours at room temperature, or soak in the fridge (Centre for Food Safety).
• Airtight storage. Health Canada warns that fresh mushrooms stored unrefrigerated in an airtight container may allow the bacteria that cause botulism to grow.
• Listeria. In the US enoki outbreak that ended in June 2020, the CDC counted 36 illnesses in 17 states, 31 hospitalisations and 4 deaths, including 6 pregnancy-associated cases with 2 fetal losses, linked to enoki from one supplier in the Republic of Korea. The Centre for Food Safety notes Listeria can grow at temperatures as low as 0°C but is destroyed by normal cooking.

Health Canada estimates that over 4 million Canadians get food poisoning each year, many cases preventable by proper handling.

• Buy fresh, firm mushrooms without damage or spoilage, in packs covered with perforated film (Health Canada), and check the use-by date (Centre for Food Safety).
• Store loose mushrooms in a paper bag in the fridge, and prepackaged ones in their packaging or a paper bag for up to five days (Health Canada).
• Freeze only after steaming or sautéing; they keep 8 to 12 months (Health Canada).
• Wash your hands for at least 20 seconds, rinse mushrooms under cool running water just before cooking, and pay attention to the underside of the caps (Health Canada).
• Keep apart uncooked mushrooms and cooked food (Centre for Food Safety).
• Cook thoroughly. The CDC's Montana report concluded that morels should be cooked before eating, and the Centre for Food Safety advises washing and cooking mushrooms thoroughly.

The Centre for Food Safety's first rule is not to pick wild mushrooms for eating, because edible and poisonous species can look alike and grow in the same place. Poison Control adds that cooking does not make a poisonous mushroom safe, and that people have been poisoned by breathing in cooking fumes.

Wikipedia's mushroom-poisoning article lists folk tests that do not work:

• Bright colour means poison. Destroying angels are white.
• Animals or insects avoid poisonous ones. Death caps are often full of insect larvae.
• Poisonous mushrooms blacken silver. No mushroom toxin reacts with silver.
• Poisonous mushrooms taste bad. Survivors of amatoxin poisoning have said the mushrooms tasted good.
• Cooking makes them safe. Alpha-amanitin is not destroyed by heat.
• Rice turns red. Deaths among Laotian refugees disproved it.

• Call Poison Control at 1-800-222-1222 (U.S.) right away, or your local emergency number.
• Keep leftovers, packaging and any uncooked mushrooms; poison specialists work with mycologists to identify the species (Poison Control).
• Note what was eaten, how much, when, and whether alcohol was drunk.
• Seek medical treatment immediately if mushroom poisoning is suspected (Centre for Food Safety).
• For a pet, call your vet or the ASPCA Animal Poison Control Center at (888) 426-4435 (fee charged).

This page does not give medical advice.

Research and drafting for this page were assisted by AI and checked line by line against the sources listed below. Nothing on this page says a wild mushroom is safe to eat. If you find an error, tell us and we will correct it.