Eating moldy bread can make you sick or lead to breathing problems if you have a mold allergy. Some molds can also create dangerous substances called toxins, including aflatoxins, which can be especially poisonous. While some foods like blue cheese are meant to be moldy and safe to eat, you should assume that any mold on bread is harmful and avoid eating it. The more moldy the bread is, the higher your chances are of getting sick. Eating certain kinds of mold can be quite hazardous to your health, and the most common symptom of eating these variations of mold is nausea, though it can often be followed by vomiting. In general, it is best to throw away moldy bread at the first sign of fuzz.