Even seemingly safe mushrooms can pose health hazards, with some varieties being especially prone to soaking up moisture, which can make them go bad more quickly if they aren't stored properly. Old mushrooms can lead to botulism, a rare but fatal condition with symptoms like difficulty breathing, vomiting, and paralysis.

Old mushrooms may also carry E. coli, especially if they were improperly cleaned or served raw, and can lead to an E. coli infection causing abdominal pain, vomiting, and diarrhea. While most people recover from an E. coli infection within a week of treatment, it can take months for your digestive tract to return to normal if you develop a salmonella infection from old mushrooms.

Salmonella infection is highly influenced by your cooking method, but the age of the mushrooms can only make matters worse. To avoid getting sick from your mushrooms, keep track of how long they've been in the fridge, store them safely with proper care, and throw them out if they become slimy, smelly, wrinkly, or darker in color.