When you find mold on cheese or a strange smell on raw chicken, the question becomes: throw it out or take the risk? A toxicologist explains that spoiled foods can contain dangerous toxins, and knowing the difference between harmless and hazardous spoilage is essential.

Grains and nuts: a major concern

Nuts and grains often develop mold from fungi such as Aspergillus flavus and A. parasiticus, which produce aflatoxins — potent carcinogens known to damage DNA and increase liver cancer risk.
Fusarium molds on wheat, barley, and corn can produce trichothecenes and fumonisin B1, which damage cells and may harm the liver and kidneys.

If grains or nuts look moldy, discolored, or smell musty, they should be thrown away — the toxins have no safe level.

Fruits: toxins beneath the surface

Moldy fruit can produce patulin, a toxin linked to organ damage. Because mold filaments can penetrate deeply, cutting off moldy areas of soft fruits is unsafe. Hard fruits are somewhat safer, but still risky.

Cheese: when mold is expected vs. when it’s dangerous

Some cheeses rely on mold for their flavor (like blue cheeses or Brie).
But unwanted molds — especially greenish-black or reddish molds — may produce harmful toxins such as cyclopiazonic acid, which can affect nerve and muscle function.

• Soft cheeses (ricotta, cottage cheese, cream cheese): discard at any sign of mold.

• Hard cheeses: cutting away an inch around the mold is safer, as mold doesn’t spread as deeply.

Meat: where bacteria, not mold, are the real threat

Spoiled meat may show discoloration, a slimy surface, or a sour smell — but dangerous bacteria can be present even without obvious signs.

Bacterial toxins can survive cooking temperatures. Common culprits include:

• E. coli → shiga toxin → kidney damage

• Campylobacter → gut infection → possible Guillain–Barré syndrome

• Salmonella → severe intestinal inflammation

• C. perfringens → toxin-induced diarrhea

• C. botulinum → botulinum toxin, one of the most lethal known poisons

Spoiled meat should never be consumed — heat may kill bacteria, but not their toxins.