Favism is an acute episode of red blood cell destruction triggered when a person with a specific enzyme deficiency eats fava beans or even inhales fava bean pollen. The underlying condition, called G6PD deficiency, affects over 443 million people worldwide. Most people with G6PD deficiency live their entire lives without a crisis, but exposure to fava beans (also called broad beans) can cause a rapid, sometimes dangerous breakdown of red blood cells known as hemolytic anemia.
How Fava Beans Damage Red Blood Cells
Fava beans contain two natural compounds called vicine and convicine. When digested, these break down into powerful oxidizing agents. Normally, your red blood cells can neutralize these oxidizing chemicals using an enzyme called glucose-6-phosphate dehydrogenase, or G6PD. This enzyme acts like a built-in defense system, protecting the delicate membrane of each red blood cell from oxidative damage.
In people who don’t produce enough G6PD, that defense system is either weak or essentially absent. The oxidizing byproducts of fava beans attack the cell walls of red blood cells directly, causing them to rupture and release their contents into the bloodstream. This mass destruction of red blood cells is called hemolysis, and it’s the core event behind a favism crisis. The severity depends on how much enzyme activity a person has and how many beans they consumed relative to their body weight.
Who Is at Risk
G6PD deficiency is inherited through the X chromosome, which makes it far more common and more severe in males. Males carry only one X chromosome, so a single altered copy of the G6PD gene leaves them with no backup. Females have two X chromosomes, which typically means one normal copy can compensate for an altered one. However, many females with one altered copy still develop symptoms because of a process called X-inactivation, where the body randomly shuts down one X chromosome in each cell. When this inactivation skews toward silencing the normal copy, a woman can end up with enzyme levels just as low as an affected male.
The condition is most prevalent in South Asia (which accounts for roughly 138 million cases), sub-Saharan Africa, the Middle East, and Mediterranean Europe. These regions overlap heavily with areas where malaria is or historically was common, and that’s not a coincidence. G6PD-deficient red blood cells appear to be a less hospitable environment for the malaria parasite, which may not replicate as efficiently inside them. People who carried the gene variant were more likely to survive malaria outbreaks and pass the trait on, a pattern similar to sickle cell trait.
Symptoms and Timeline
A favism crisis doesn’t happen immediately. Symptoms typically begin one to three days after eating fava beans, though the window can stretch from 24 hours to five days. In some reported cases involving repeated daily consumption, symptoms appeared after a week or more of continuous intake.
The hallmark signs include:
- Dark or discolored urine, often the first thing people notice, caused by hemoglobin released from destroyed red blood cells
- Jaundice, a yellowing of the skin and eyes from the buildup of bilirubin as the body processes the debris of broken-down cells
- Pallor and fatigue, reflecting the sudden drop in healthy red blood cells
- Rapid heart rate, as the heart works harder to circulate the remaining oxygen-carrying cells
- Abdominal pain, nausea, vomiting, and dizziness
In more severe episodes, the spleen and sometimes the liver enlarge as they work overtime to filter damaged cells from the bloodstream. Infants are particularly vulnerable because even a small amount of fava beans represents a large dose relative to their body weight. Deaths from favism, while rare, have been documented in infants for this reason. Kidney failure has been reported in adults during severe crises, and a small number of children have experienced vision problems as a complication.
How It Is Diagnosed
Favism itself is diagnosed based on the combination of symptoms and recent fava bean exposure, but the underlying G6PD deficiency is confirmed through a blood test that measures enzyme activity. The WHO classifies severity into four levels based on how much enzyme function remains. People with less than 10% of normal activity fall into the most severe categories. Males with activity below 30% of normal are considered G6PD deficient, while females fall into a gray zone: below 30% is deficient, above 80% is normal, and anything between 30% and 80% is classified as intermediate.
One important testing caveat: enzyme levels can appear falsely normal right after a hemolytic crisis. That’s because the oldest, most enzyme-depleted red blood cells are the first to be destroyed, leaving behind younger cells with higher enzyme levels. If G6PD deficiency is suspected after a favism episode, testing is often repeated a few weeks later once red blood cell populations have stabilized.
Treatment During a Crisis
There is no medication that stops hemolysis once it starts. Treatment focuses on supporting the body while it recovers. In mild cases, staying well hydrated and avoiding further exposure to fava beans may be enough. The body ramps up production of new red blood cells, and symptoms gradually resolve over several days.
Severe episodes require hospital care. If red blood cell counts drop dangerously low, blood transfusions are used to stabilize oxygen delivery to organs. Children and infants with significant jaundice may need phototherapy to help break down excess bilirubin. Most people recover fully within one to two weeks, but kidney function and overall blood counts are monitored closely during that time.
Triggers Beyond Fava Beans
Fava beans are the most well-known trigger, but they’re not the only one. Hemolytic episodes can occur after eating fresh fava beans, dried beans, or even after inhaling pollen from fava bean plants during flowering season. For people living near fava bean fields, spring can pose a real risk.
Several medications also trigger the same kind of oxidative damage to G6PD-deficient red blood cells. The most commonly cited include primaquine (an antimalarial drug), nitrofurantoin (a urinary tract infection antibiotic), dapsone (used for certain skin conditions), methylene blue (used as a medical dye), and several sulfonamide antibiotics. Rasburicase, a drug used to manage high uric acid levels, is another well-established trigger. Infections and physical stress on the body can also provoke hemolytic episodes in susceptible individuals, sometimes with no dietary trigger at all.
Living With G6PD Deficiency
G6PD deficiency is a lifelong condition with no cure, but it is entirely manageable with awareness. The practical reality for most people is straightforward: avoid fava beans in all forms, carry a list of medications that can trigger hemolysis, and make sure every healthcare provider you see knows about the deficiency before prescribing anything. Many people with G6PD deficiency go decades between episodes, or never have one at all, simply by steering clear of known triggers.
Parents of children diagnosed with the condition should be especially cautious during weaning and early childhood, when accidental exposure is most likely and the consequences relative to body size are greatest. In regions where the deficiency is common, newborn screening programs are increasingly available and can identify at-risk infants before their first exposure ever occurs.