As hungry Italians at the Festival for the Fava Bean lined up in a field in the Roman countryside to order fava and pecorino cheese, fava and porchetta, cream of fava on top of pasta or simply brown bags loaded with fresh fava, the manager of an adjacent garden spoke of the witch-fingered legume with dread.

“We search for them and rip them out,” said Francesco Urso, 72, pointing at a sign that read “The planting of Fava is banned.” The leathery green pod bulging with indented oval beans may be delicious, great for the soil and a cherished Roman springtime snack, Mr. Urso said, but the issue was one of life or death.

“Favism,” he said.

While many Romans celebrate the fleeting May fava season and the coming of spring with fava-heavy picnics outside the city walls, sufferers of favism live in fear. For those with the blood disorder — which Lucio Luzzatto, a leading scientist in the field, said spread throughout the Mediterranean, Africa and the Middle East because it offered some protection against malaria — exposure to fava beans can cause acute hemolytic anemia; induce jaundice; enlarge the spleen; and prompt heart failure and death.

Around Rome this time of year, warning signs reading “In this place fresh fava are served” are taped to restaurants and markets. The near-death experiences of favism-afflicted celebrities go viral. “In the period of the fava, be careful,” implored Ginevra Pisani, a television starlet who described on her social media feed turning “completely yellow, green” and fainting as her “red blood cells committed suicide.”

“And I thought they were good for you, these fava,” she added bitterly.

Many Italian towns have introduced ordinances banning the cultivation of fava beans within hundreds of meters of schools or the homes of the vulnerable, as some favism sufferers say a mere whiff of the insidious fava pollen can set off an attack.

Sardinia, the southern Italian island where about 10 percent of the population has favism, with the number hitting 13 percent in the south, has developed some remedies over the years.

“To heal me when I was little, they laid me down and put me up to my face in ox crap,” said Beatrice Brundu, 78, from the small Sardinian town of Perdasdefogu. “And it cured me. Now, they just give me pills.”

But despite the prevalence of the disease, fava beans are unavoidable throughout Italy, especially in Rome in May. They tangle in fresh market crates, freshen up dishes laden with guanciale, simmer in the beloved vignarola fresh vegetable stew. (“It’s May 1,” announced a waiter at Osteria la Gensola in Rome, “we have a rigatoni alla vignarola.”) They are also, according to the city government’s Fava and Pecorino page, “tied to the ancient usage of the commemoration of the dead.”

Still, in May, the fava bean, bursting and green, is a sign of life.

At the Roman trattoria Da Felice, wine-and-sun drenched diners ordered pasta with fava beans, peas and guanciale as Cesare Murtas, a manager who is from Sardinia, looked on beside the front door’s beware-of-fava-beans sign. “My son has it,” said Mr. Murtas, 52, referring to the disorder. He said he had taught his son from an early age to stay away from the beans. “He wears dog tags that say he has favism in case he gets into a car accident.”

Around the corner at Checchino, another venerable Roman institution with a warning on the door, the owner, Francesco Mariani, 62, said he had once employed a chef from Sardinia who had favism. “He couldn’t even touch them,” he said of the beans. “Someone else had to cook those dishes.”

But he found the notion of not offering fava in May ridiculous, and argued that the entire culture of allergies and intolerances had gotten way out of control, with people expecting lab-level decontamination efforts for gluten, lactose and beans.

“Don’t go to a Roman restaurant,” he said. “Go get sushi.”

Fava, one of the oldest cultivated crops stretching back to at least 6,000 B.C., has long been a source of protein and anxiety across the region.

The Greek philosopher Pythagoras, father of the a² + b² = c² theorem, considered the fava a symbol of death. He is said to have preferred to risk fatally facing his enemies rather than run into a field of fava. His cult of vegetarian geometry enthusiasts believed that the fava bean held the souls of the dead, or that their hollow stems provided elevator service up from Hades.

Ancient writers also suggested that they disliked fava because they resembled genitalia, or a fetus, or because they caused flatulence, which drained the breath of life. Or, as Scientific American put it, because they “believed a chewed bean smelled like the blood of a murder victim when left in the sun.”

In the Middle Ages, draught-stricken Sicilians prayed to Saint Joseph for rain and found salvation from famine in fava beans, which are still placed on church altars and venerated with cakes in the shape of the “beans of the dead” on All Souls Day.

The ancient Romans considered fava beans so connected to death and decay that some priests could not touch them, and they were a mainstay on funerary feast menus. For decades, tipsy Romans sang “Fiori Trasteverini,” about how everything in “Roma bella” is for sale, including St. Peter’s, the sky and the air, “but the Roman fava we can give away.”

The hundreds of Romans at the fava festival last Sunday, in Castel di Leva, knew what they wanted. Downy green mountains of discarded fava pods stacked up on long wooden tables like science-fair volcanoes. As Romans shelled and inhaled the beans, there wasn’t a warning sign at the fair. “It’s a Festival of the Fava,” said Francesco Galli, 47, the event’s organizer. “If you’re allergic, maybe don’t come.”

At one table, Carmelina Antonini, 74, loaded the empty pods into her bag. “Nothing gets thrown out,” she said, telling her dubious husband and friends that she would boil them and then fry them with garlic and hot pepper.

She and her friends compared notes about people they had known who had favism (“he got an anaphylactic shock”), and she recalled that it was once a cause for discharge from the military service.

“Why?” asked her friend Emilia Cucci, 77, “because the army was picking fava beans?”

Ms. Cucci then recalled a traumatic incident when she was served fava beans — meant to be tender and buttery — that were instead “as hard and small as a pebble,” leading her to launch them in protest.

Lately, she said, that while free of favism, she worried that she suffered from some other mysterious allergy that led her to “sneeze four, five, six times.”

“Who knows?” her husband interrupted.

“I’m talking,” she said. “Maybe it’s the husband.”

A few yards away, Sara Lauteri, 29, a fava vendor, stood behind heaping piles of pods, advertising how they were “super fresh, picked this morning.” She stuffed them into brown bags for customers and said no favism sufferer had ever been reckless enough to approach her.

“Their red globules practically explode,” she said.

Paola Romani, 59, nodded in agreement.

“It’s a nasty disease — it takes you by the throat,” she said. Then she opened a pod, popped some beans into her mouth and bought a bag to go with her brick of pecorino. “May,” she said with a shrug, “is fava.”

Gaia Pianigiani contributed reporting.