Eaten mushrooms may cause stomachache, vomiting and diarrhea when consumed in large amounts. Amanitas (death caps) are one of the most poisonous varieties and should be treated as such; their appearance makes them hard to differentiate from nonpoisonous varieties, while their toxin is not destroyed through cooking either. Poisoning from death caps typically begins with nausea or stomach ache before progressing further to blood disorders, heart and liver damage or even death.

Mushrooms may cause gas because they contain FODMAPs (fermentable oligosaccharides, disaccharides, monosaccharides and polyols) which are easily fermented in the large intestine by bacteria, leading to symptoms like gas, bloating, abdominal pain and bowel changes for those sensitive to FODMAP foods such as Irritable Bowel Syndrome (IBS). Mushrooms also contain natural sugar alcohols like mannitol that draw water into large intestine and cause looser stooling for some people.

To prevent mushroom-related gas, ensure your mushrooms are fresh and have been stored appropriately. Avoid buying contaminated mushrooms, and check your stash regularly for signs of spoilage such as rancid smell or mold growth. Any expired mushrooms should be thrown away as they could contain harmful bacteria; to preserve their quality longer than necessary store them in the fridge in a paper bag for best results.