What Happens If You Eat Moldy Bread?

It’s 3:00 a.m. You’re craving a peanut butter and jelly sandwich — or maybe a grilled cheese. You open the bread bag, and — ugh! — the bread’s edges are covered in blue mold. As you hesitate, wondering whether to toss it, you ask yourself, what happens if you eat moldy bread?

You recall that penicillin is made from mold [source: NLM]. So, is it safe to eat moldy bread? Think again. Let’s take a closer look at what could happen if you go ahead and consume that moldy slice.

Learn About Mold Spores

Molds are related to mushrooms. When you examine molds under a microscope, they often resemble miniature mushrooms, with stalks topped by tiny spores.

These spores are responsible for the vibrant colors of molds — such as the blue-green tint that marks your now unusable loaf of bread [source: USDA].

The Dangers of Mold

While molds can be visually striking, they pose risks. With hundreds of thousands of species, many molds trigger allergic reactions and respiratory issues. Some even produce mycotoxins, a harmful toxin that can cause illness in humans, animals, and livestock.

And do you know where one of the most notorious mycotoxins, aflatoxin, grows? You guessed it: on grains and nut crops, both key ingredients in many types of bread [source: USDA].

Aflatoxin, a cancer-causing mold found worldwide, is one of the most well-researched and closely monitored molds. However, despite its scrutiny, it hasn't been completely wiped out — though manufacturing facilities worldwide are closely watched to ensure aflatoxin levels stay within permissible limits [source: USDA].

The Hidden Risks of Mold

Now, back to that 3:00 a.m. slice of bread with mold along the edge. What if you simply cut off the moldy section and eat the rest? Surely, that’s safe, right? Unfortunately, no.

What you see on the edge of the bread could just be the visible part of the mold. From its stalks, mold can send roots deep into the bread. These roots are where mycotoxins like to thrive. Plus, invisible bacteria that could also make you ill might be hitching a ride with the bread mold [source: Nelson].

While your high school science teacher was correct in saying that penicillin comes from mold, attempting to extract this bacteria-fighting substance from moldy bread is not advisable.

Next time you're tempted by a PB&J or grilled cheese, take a careful look at your bread. If you notice any mold on it, it might be wise to skip the snack, especially in the middle of the night.

How to Prevent Mold

Here are some tips to keep your bread fresh longer, so you can avoid the worry of eating moldy bread in the future.

To keep bread fresh, store it in a breathable container like a cloth bag, clean towel, or paper bag, and place it in a dry cupboard or bread box.

If you aren't able to consume an entire loaf in just a few days, slice it up and store the pieces in the freezer, where it will stay fresh for up to six months [source: Save the Food]. You can then easily toast the frozen slices whenever you're ready.