Imagine eating your daily bread—and feeling as though your body were burning from the inside.

Your hands and feet begin to ache. The pain becomes unbearable. Your skin darkens. In severe cases, the tissue dies.

For centuries, Europeans described a mysterious affliction using names that evoked fire, punishment, and suffering.

One of those names was St. Anthony’s Fire.

And behind some of the most frightening outbreaks was something hidden in an ordinary food: bread.

A Poison Hidden in the Harvest

The culprit was ergot, a fungus that infects cereal grains, particularly rye.

Known scientifically as Claviceps purpurea, it produces dark, hardened structures that can contaminate harvested grain.

When contaminated rye was ground into flour and baked into bread, people could unknowingly consume toxic compounds called ergot alkaloids.

The resulting illness is known as ergotism.

In communities that depended heavily on rye, contaminated harvests could expose many people to the same poison.

The danger wasn’t necessarily obvious. The food people relied on for survival could also make them desperately ill.

The Disease That Felt Like Fire

Ergot poisoning can take different forms.

In gangrenous ergotism, the toxins can severely restrict blood flow, particularly to the extremities.

Victims may experience intense burning pain, numbness, and tissue death. In the worst cases, fingers, toes, or entire portions of limbs can become gangrenous.

Another form, convulsive ergotism, can cause muscle spasms, seizures, and disturbances of perception or mental state.

These were not supernatural attacks. They were devastating effects of poisoning.

But for people who did not understand the chemistry of contaminated grain, the suffering could seem inexplicable.

Why St. Anthony?

The disease’s association with St. Anthony developed through medieval religious traditions.

People suffering from burning illnesses sought spiritual protection and care associated with the saint. The Order of St. Anthony became known for caring for patients with severe diseases, including gangrenous conditions.

The name survived long after the medieval world that produced it.

There is, however, an important historical complication.

Not every illness described as St. Anthony’s Fire can confidently be identified as ergotism.

Medieval writers used overlapping names for different diseases, and modern historians caution against automatically diagnosing every account of burning pain or gangrene as fungal poisoning.

The documented medical reality of ergotism is clear. The diagnosis of individual medieval outbreaks is sometimes less certain.

The Strange Connection to Other Historical Mysteries

Ergot has also appeared in theories about two other extraordinary events.

Some researchers have suggested it might help explain the Dancing Plague of 1518, when people in Strasbourg reportedly danced uncontrollably.

Others have proposed that ergot poisoning contributed to the unusual symptoms reported during the Salem witchcraft crisis of 1692.

Both theories remain disputed.

Neither event has been conclusively explained by ergot poisoning, and historians have raised substantial objections to those proposed connections.

That distinction matters.

We know ergot-contaminated grain can cause terrible illness. We do not know that it caused those particular episodes.

The Horror Was Real

The most unsettling part of this history is not the supernatural explanation.

It’s the ordinary one.

A fungus growing in a field could contaminate the harvest, enter the flour, and turn a family’s daily bread into a source of devastating illness.

People searched for explanations in religion, medicine, and the mysterious forces they believed surrounded them.

The danger, however, could begin with something as familiar as dinner.

Sometimes history’s strangest horrors were hiding in plain sight.