What Happens If You Eat Moldy Bread?

What Happens If You Eat Moldy Bread
If you eat moldy bread, chances are good you’ll feel fine or slightly nauseous. However, some types of mold are dangerous and can make you sick or potentially kill you.

No one wants to eat moldy bread, but you don’t want to be wasteful, either. Is it okay to scrape off the mold and eat the rest of the slice? Does one bad slice ruin the entire loaf? Here’s a look at what mold is, whether it’s safe to eat moldy bread, what happens if you eat it, the types of mold on bread, and how to prevent it from growing.

What Can Happen?

Except for grossing you out, eating or smelling moldy bread usually causes no significant harm. The most common effect is nausea. Coughing, sneezing, vomiting, headache, diarrhea, and fever may also occur. However, people with weakened immune systems, allergies, or asthma and pregnant women are at greater risk of suffering more severe effects. Some molds can cause asthma attacks, sinus and lung infections, other organ infections, and cancer. Certain types of mold can cause neural tube defects in a developing fetus. Although it’s rare, eating moldy bread can cause death.

You should never knowingly eat or smell moldy bread, but if you do, you’ll probably be fine. However, moldy bread can cause allergic reactions, cancer, and other life-threatening conditions.

What Is Mold?

Mold is a type of fungus, like mushrooms and yeast. Fungi break down the material they grow on so they can absorb nutrients. Mold lives in colonies that reproduce by sending out filaments and spores. So, it spreads through a material directly and from the transport of spores through the air. Some types of mold produce toxins that inhibit the growth of other organisms. Some of these toxins, called mycotoxins, are harmful to humans and other animals.

Types of Bread Mold and Health Risks

Slice of Moldy Bread
Color isn’t a reliable indicator of the type of mold on bread. Some species change their appearance depending on where they are in their life cycle. (photo: Vincent van Zeijst, CC4.0)

Bread hosts many types of mold, including Aspergillus, Cladosporium, Fusarium, Mucor, Penicillium, and Rhizopus. Mold spores are always present in the environment. Some common bread mold species include:

  • AspergillusAspergillus forms fuzzy patches on bread. The spots can be yellow, pale green, or multicolored. Aspergillus is common in air, so most people eat and breathe a small amount of this fungus every day without getting sick. Eating a moldy patch of bread or sniffing moldy bread exposes a person to a much higher Aspergillus concentration than normal and can cause a stuffy nose, headache, facial pain, fever, and sinus infection. However, people with allergies or weakened immune systems can develop aspergillosis, which is characterized by lung infections and infections in other organs.
  • Black bread mold (Rhizopus stolonifer) – Black bread mold occurs on every continent. It usually appears as fuzzy blue or green spots, which develop black centers. Eating black mold can cause nausea, vomiting, and indigestion. Inhaling the spores can cause an allergic reaction, worsen asthma, and trigger anaphylactic shock in sensitive individuals.
  • CladosporiumCladosporium forms deep green to black splotches on bread. This type of mold has a more noticeable odor than most other species. Because of the “moldy” smell, eating this mold often causes vomiting. Some Cladosporium molds release mycotoxins, but usually this fungus doesn’t cause a significant problem unless a person is allergic to it.
  • FusariumFusarium is a filamentous fungus. Some species are harmless. In fact, Fusarium naturally occurs as a part of skin flora. The species Fusarium venenatum is produced commercial for use as food under the name Quorn. However, Fusarium often causes food allergies and is responsible for opportunistic infections, even in otherwise healthy individuals. The main toxins produced by members of this group are flumonisins and trichothecenes. These mycotoxins are so potent that they can be weaponized for biological warfare. Effects of exposure include abdominal pain, diarrhea, vomiting, fever, chills, gastrointestinal ulcers, and bleeding into the skin. Accidental exposure, from bread baked with Fusarium-contaminated wheat, resulting in a 60% mortality rate in the 1930s and 1940s in the Soviet Union.
  • MucorMucor forms black dots on bread and other baked goods that quickly grow into gray or white patches. Mucor is an allergenic mold, implicated in allergic reactions, asthma, and potentially anaphylaxis. Eating or inhaling it can lead to mucormycosis, which is a rare but dangerous infection that can spread into the lungs and brain. Mucormycosis mainly affects people with compromised immune systems when they eat or inhale it, but the spores can also enter the skin through a cut.
  • PenicilliumPenicillium forms pale fuzzy patches on bread that may be blue, gray, or white. One species of Penicillium produces the antibiotic penicillin. Others are used to intentionally flavor blue cheese and other foods. But, some types of Penicillium release potent mycotoxins (e.g., orchratoxin A) that can cause cancer and other illnesses. While this mold might not have an immediate effect, prolonged exposure can be dangerous.

Throw Out Moldy Bread

According to the Food Safety and Inspection Service of the United States Department of Agriculture (USDA), you shouldn’t try to salvage moldy bread. Even if you only see mold on the edge of one slice of bread, mold spores and hyphal filaments have already permeated the entire loaf. This is also true of other porous foods, including any baked goods, sour cream, soft cheese (except the kind meant to have mold), soft fruits, jelly, nuts, and meat.

  • Don’t sniff moldy bread. Inhalation of mold isn’t any better for you than eating it and may be more likely to provoke an allergic reaction.
  • Toasting moldy bread doesn’t make it safer.
  • Don’t feed moldy bread to pets or livestock. Animals are just as susceptible to mycotoxins as humans are.
  • Seal moldy bread in plastic wrap before disposal to minimize the amount of airborne mold.

How to Keep Bread From Getting Moldy

The shelf-life of fresh bread made without preservatives and stored at room temperature is usually three to four days. Bread from a store typically contains calcium propionate, sorbic acid, or other preservatives that deter mold growth and extend its shelf-life. Preservative-free bread can be vacuum-sealed to keep out mold spores until the package is opened. Sourdough bread contains lactic acid bacteria that help it resist mold longer than other bread. But, bread naturally picks up spores from the air, so eventually it molds. Warmth and humidity encourage mold growth, so proper storage is your best defense against bread mold.

  • Keep bread covered. Let fresh bread cool before covering it, to avoid trapping moisture. Otherwise, package bread to minimize its exposure to mold spores in the air.
  • Keep bread dry. If you see moisture droplets inside the packaging, you can clean it with a paper towel.
  • Keep bread cool. Refrigerating or freezing bread slows mold growth. Unfortunately, it also changes its texture and can make it too dry. Freezing generally has less of a negative effect than refrigeration.


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