It’s 3 a.m. and you’re craving a peanut butter and jelly sandwich. You open the bread bag and — ugh! — the bread is blue with mold along one edge. As you’re standing there, trying to decide just how badly you want that sandwich, you may try to convince yourself that it’s okay because penicillin is made from mold. That makes it okay to eat, right? Think again. Here’s the skinny on what might happen if you eat moldy bread. While molds may be thought of as harmless, they can actually cause allergies and respiratory problems. Back to the 3 a.m. piece of bread with the mold on one edge. What if you cut off the moldy bits and just eat the rest? Surely that's okay, right? Wrong. What you see on the edge of bread may be only the tip of the mold. From the stalks, mold can shoot roots down into the bread. These roots are where the mycotoxins like to grow. In addition, invisible bacteria that can also make you sick may be tagging along with the mold. So, while your high school science teacher was right about penicillin being made from mold, it's not a good idea to try to get this bacteria-fighting agent from moldy bread. The next time you're craving a PB&J in the wee hours, check out your bread carefully. If there's mold on the surface, you may be better off with a different late night snack.