What Is the Toxin in Buckwheat?

November 13, 2025 •

4 min read

Though buckwheat is generally considered a healthy, gluten-free pseudo-cereal, it does contain a phototoxic compound called fagopyrin. This natural substance is responsible for a condition known as fagopyrism, a photosensitivity reaction that primarily affects livestock but can also impact humans under specific, rare circumstances.

Quick Summary

The toxin in buckwheat is fagopyrin, a phototoxic substance that can cause photosensitivity, known as fagopyrism, mainly in animals but also in humans who consume large amounts of un-milled plant parts and are exposed to sunlight.

Key Points

Fagopyrin is the primary toxin: Buckwheat contains a phototoxic substance called fagopyrin, concentrated mainly in the green plant parts like leaves and flowers.
Toxicity causes photosensitivity: When ingested in high enough amounts and followed by exposure to sunlight, fagopyrin causes a reaction called fagopyrism, leading to skin inflammation.
Common buckwheat foods are safe: Standard commercial buckwheat foods like flour and groats contain negligible levels of fagopyrin due to milling and heat processing.
High-risk items are sprouts and extracts: A higher risk exists with large-scale consumption of raw sprouts or concentrated extracts from the green parts of the plant.
Contamination is a rare but severe risk: In rare cases, buckwheat can be contaminated by other toxic plants, such as Datura spp., which contain dangerous tropane alkaloids.
Allergic reactions are separate from toxicity: Some people may develop a standard food allergy to buckwheat, which is different from fagopyrism.

Fagopyrin: The Phototoxic Compound

Fagopyrin is the primary phototoxic substance naturally present in buckwheat plants, particularly in the leaves, flowers, and sprouts. This compound, a type of naphthodianthrone, is structurally similar to hypericin, another phototoxic compound found in St. John's Wort. When ingested and absorbed, fagopyrin circulates in the bloodstream and can react with ultraviolet (UV) light, causing damage to blood vessels and leading to a condition called fagopyrism.

How Fagopyrin Causes Photosensitivity

Photosensitivity reactions occur when a substance in the body makes the skin more sensitive to light. The process unfolds in several steps:

Ingestion: Fagopyrin is consumed, typically from buckwheat plant parts like green foliage or sprouts, rather than the ripe grain.
Absorption: The compound is absorbed into the gastrointestinal tract and travels through the bloodstream.
UV Activation: When exposed to sunlight, particularly UV rays, the fagopyrin molecules become activated.
Cellular Damage: The activated fagopyrin then produces radiant energy in the form of fluorescence, which damages the blood vessels in the skin, especially in unpigmented areas.

The Condition of Fagopyrism

Fagopyrism is a photosensitivity disorder resulting from the ingestion of fagopyrin-rich buckwheat plant matter. While it is rare in humans, documented cases of poisoning have historically occurred in livestock, particularly white or white-spotted animals that graze on buckwheat foliage.

Symptoms in Humans and Animals

Symptoms of fagopyrism differ depending on the severity and can affect both animals and humans.

In Animals (Livestock): Mild cases can cause itching and erythema (redness) on the head and face, especially in areas with light-colored skin. More severe symptoms can include skin sloughing, convulsions, paralysis, and even death.
In Humans: Human cases are extremely rare but can manifest as skin inflammation, cold sensitivity, and tingling or numbness in the hands after high exposure to fagopyrin and sunlight. Consuming high amounts of fagopyrin-rich extracts, flowers, or sprouts has also been associated with this risk.

Other Potential Toxins: Tropane Alkaloids

In very rare instances, buckwheat-associated toxicity can come from contamination rather than from fagopyrin. Buckwheat can be contaminated by other plants, such as Datura spp. (thorn-apple), which contains highly toxic tropane alkaloids like atropine and scopolamine. This contamination can lead to severe neuropsychiatric symptoms, as seen in a documented case of acute psychosis after ingesting contaminated buckwheat.

Processing and Toxin Levels

The level of fagopyrin in buckwheat is significantly impacted by processing methods, which is why commercial buckwheat food products are generally considered safe for consumption.

Impact of Processing on Fagopyrin Content

Milling: The majority of fagopyrin is concentrated in the hulls and outer parts of the buckwheat seed. Milling removes these outer layers, dramatically lowering the toxin content in the groats and commercial flour.
Heat Treatment: Steaming and roasting, common processing steps, also help to reduce the fagopyrin concentration.
Sprouting: Conversely, fagopyrin levels are higher in buckwheat sprouts, particularly when grown in light.

Comparison of Fagopyrin Levels in Buckwheat Products

This table illustrates how processing affects the concentration of fagopyrin. All values are approximate and depend on the specific cultivar and processing method used.


Buckwheat Product	Fagopyrin Content (Approximate)	Relative Risk of Fagopyrism	Processing Impact
Raw Whole Grain	Moderate	Low	Initial state
Hulls/Outer Parts	High	Highest	Milling removes this part
Commercial Flour	Low	Very Low	Significantly reduced after milling
Cooked Groats	Very Low	Minimal	Heat reduces content
Raw Sprouts/Flowers	High	Higher	Sprouting can increase content
Steamed Grains	Low	Very Low	Heat reduces content significantly

Can You Safely Eat Buckwheat?

For most people, consuming commercially available and properly processed buckwheat is perfectly safe and offers numerous health benefits. The risk of fagopyrism from standard food products like flour, groats, and soba noodles is negligible due to the low fagopyrin levels.

However, there are a few important considerations:

Allergies: Some individuals may develop a buckwheat allergy, with symptoms ranging from skin rashes to severe anaphylactic shock upon re-exposure. This is distinct from fagopyrism.
Dietary Supplements: The risk increases with high consumption of un-milled or concentrated buckwheat products, such as supplements containing extracts from the green plant parts.
Cross-Contamination: As noted, consuming buckwheat products cross-contaminated with other toxic plants is a risk, although it is extremely rare.

Conclusion

While the primary toxin in buckwheat is fagopyrin, it poses a very low risk to humans who consume typical, processed buckwheat foods like groats and flour. The highest concentrations of this phototoxic compound are found in the green plant parts, such as leaves and sprouts, and processing methods like milling and heat treatment significantly reduce its presence. The condition of fagopyrism, which causes photosensitivity, is primarily a concern for livestock or for humans who consume large, concentrated amounts of fagopyrin-rich extracts. For most people, buckwheat remains a safe and healthy gluten-free option, with the rare exception of those with an allergy or in the uncommon event of cross-contamination with other toxic plants. For more detailed information on food contaminants, reputable resources like the National Institutes of Health (NIH) can be consulted.

Frequently Asked Questions

No, buckwheat flour is not toxic for humans under normal consumption. The milling process effectively removes the hulls and other outer layers where most of the phototoxic fagopyrin is concentrated, leaving only negligible amounts in the flour.

Fagopyrism in humans is extremely rare but has been associated with symptoms such as skin inflammation in sunlight-exposed areas, cold sensitivity, and tingling or numbness in the extremities. These symptoms occur only after consuming high amounts of fagopyrin and exposure to sunlight.

Yes, heat processing such as steaming and cooking significantly reduces the fagopyrin content in buckwheat. Coupled with the initial reduction from milling, cooked buckwheat groats pose a very low risk of toxicity.

Buckwheat sprouts can contain higher concentrations of fagopyrin than the seeds. Consumption of large amounts of sprouts, especially by individuals with light-sensitive skin who then get sun exposure, is where the risk of fagopyrism is highest.

Yes, some people can develop an allergic reaction to buckwheat. Symptoms can include hives, swelling, and difficulty breathing, and can be particularly severe in individuals with existing allergies to latex or rice.

Yes, livestock, especially white or partially pigmented animals, can be susceptible to fagopyrism if they graze on green buckwheat plants. Symptoms range from mild skin irritation to severe lesions or even paralysis.

Tropane alkaloids are highly toxic compounds found in some plants, like Datura spp. In very rare instances, buckwheat crops can be contaminated by these plants, leading to a different form of poisoning. This is not a toxicity inherent to buckwheat itself.