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So. You ate some moldy bread.

You made a fine looking sandwich, took a few huge bites, and then realized the bread you used was a little ... fuzzy. Oops. Good news is, most of the time, this isn’t a cause for panic.

It’s kinda gross, and you might not want to think about it too much, but in all likelihood, nothing bad will happen to you— especially if you have a healthy immune system. Still, there’s a reason experts don’t recommend finishing off that moldy loaf, so it’s best not to press your luck. Molds are a type of fungi, and some people can be allergic to them.

It’s pretty rare for something serious to happen, but one teenager actually died after eating two pancakes made with two-year-old, mold-infested mix. Even if you aren’t allergic, though, you’re still not off the hook. The other big danger with mold-contaminated foods is mycotoxins.

These are chemicals various molds make under certain conditions that are toxic to humans and other creatures. For the most part, if you consume a little bit once or twice, you’ll probably be okay. But in larger doses, or over longer periods of time, they can become an issue.

Take aflatoxin, for example, which is most commonly found in crops like corn and peanuts. We first realized it might be a problem in the 1960s when, over several months, 100,000 turkeys died in the UK from a mysterious condition dubbed Turkey X disease. Ultimately, scientists traced the poultry massacre to aflatoxin contaminating the animal feed.

Today, we also know aflatoxin increases risk of liver cancer in humans, so it’s not something you want on your toast. Other dangerous mycotoxins include ochratoxin, which targets the kidneys and is often found in corn or barley products, and fumonisins, which can cause birth defects and are also found in corn. Right now, we know of about 400 or so mycotoxins in total.

For the most part, though, they’re not too concerning in countries that do food safety tests and keep tabs on these sorts of things. They tend to contaminate raw grains and animal feeds rather than things you’d stick in your mouth directly, but they can cause outbreaks and are a real health hazard in developing nations. Because you could get sick, the rule of thumb is to throw away food that has any mold on it if it’s soft.

This applies to things like bread, and also soft cheeses, meats, and dips. That’s because molds grow in microscopic thread-like branches called hyphae, and in soft foods, it’s easier for them to spread. By the time you have a colorful patch of fuzzy spores on your bread, it’s likely that the filaments run deep.

If the food is harder, like a hard cheddar, it’s less likely that those hyphae have infiltrated the whole cheese. So, if mold is on just a small area, you can cut around it, but be generous. The same advice goes for firmer fruits and veggies like carrots or large strawberries.

Toss or cut out the moldy section, rinse the rest, and enjoy. But of course, if the whole item is covered in fur, you’ll want to stay away. Finally, if you see mold on food, there’s a good chance it’s also loaded with bacteria by that point.

Which means mycotoxin or not, you could still get sick. So it’s better to play it safe, and find another snack. Sorry.

Thanks for asking, and thanks to all of our patrons on Patreon who keep the questions coming! If you have a burning question, or if you’d like to help us keep answering them, you can go to patreon.com/scishow. [OUTRO ♪].