You go to make a sandwich, and you see a spot of green on a piece of bread.
It’s mold. No big deal, right? You’ve dealt with this before. Simply cut off the moldy section and proceed as planned.
Not so fast. According to the United States Department of Agriculture, you could be taking a serious health risk.
“We don’t recommend cutting mold off of bread because it’s a soft food,” says Marianne Gravely, a senior technical information specialist for the United States Department of Agriculture. “With soft food, it’s very easy for the roots [of the fungi], or the tentacles, or whatever creepy word you want to use, to penetrate.”
That means that you’re only cutting out part of the mold, not all of it.
That’s kind of a big deal, according to the USDA.
Mold is mainly dangerous because it creates mytotoxins, poisons that can cause respiratory distress, vomiting, and other serious issues. Mold is a major source of food poisoning, and ingesting mold can even have fatal consequences in rare circumstances.
Of course, mold isn’t the only food affected by mold. In fact, spores are everywhere; however, bread is especially susceptible to mold infiltration thanks to its porous, slightly moist surface.
Mold spores can easily spread through an entire loaf, sometimes within a few hours, but it isn’t visible until there’s a large concentration of mold spores in a single place. That’s when those green, brown, and black spots start showing up. Therefore, the health risk isn’t confined to those spots (although those are the riskiest bits to eat).
The exact health risks vary depending on the type of mold on your food.
Fungi from the genus Aspergillus, for instance, can cause a disease in people with immune deficiencies. Penicillium is the genus of fungi that creates penicillin, but the kind that grows on bread can trigger serious allergic reactions.
According to the USDA, there are more than a dozen other common food mold genuses, not to mention hundreds of individual species; without a microscope, you probably won’t be able to definitively identify any of them.
As such, you shouldn’t assume that any mold is safe—even if you’ve eaten it before.
So, what’s the best way to avoid moldy bread?
Simple: Only buy what you need. Don’t load up on bread at the beginning of the week if you aren’t planning on making that sandwich until Friday. This is especially important with fresh breads from the bakery, since they don’t contain the same powerful preservatives as mass-produced commercial loaves.
You can also limit the number of mold spores in your kitchen by cleaning regularly. Store food properly, paying special attention to fruits and vegetables. Clean your refrigerator every few months, and try to keep your home’s humidity level at 40 percent or below.
Finally, don’t just throw away the moldy part of your bread—there’s more mold than what you see on the surface.
“I’m sure some people would really want to press the situation, but bread is cheap,” Gravely told NPR. “Go buy some more.”