Some bacteria can be resistant even to incredibly hostile environments (like your stomach, a volcano, or freezing temperatures, etc.). So your stomach's acid might not be enough to kill some kinds of bacteria that may have grown on/contaminated your food.
Thefoodiemaniac t1_j20x1fx wrote
Reply to ELI5 Why does eating food that is "off" make you sick, when you are essentially putting it in an acid bath that should destroy any greebies? by anti_queue
Some bacteria can be resistant even to incredibly hostile environments (like your stomach, a volcano, or freezing temperatures, etc.). So your stomach's acid might not be enough to kill some kinds of bacteria that may have grown on/contaminated your food.