The buckwheat plant goes by the scientific name Fagopyrum esculentum, and is cultivated for the grain-like seeds that it produces. The cooked buckwheat seeds can be a healthy addition to your pet’s diet, especially as a gluten free alternative to treats or food made with wheat. The rest of the plant contains fagopyrin, a compound that induces a painful reaction to the sun’s rays known as photosensitivity. This can cause a fear of sunlight (photophobia), lesions, and in severe cases, necrosis of the skin.

The toxin fagopyrin, produced by the buckwheat plant, can cause hypersensitivity to sunlight, painful lesions, and the development of necrotic skin tissues in canines when ingested in large amounts.

The symptoms of poisoning by buckwheat greens are caused by the photosensitivity that is induced by the fagopyrin in the plant. Symptoms of photosensitivity will noticeably diminish when not exposed to UV light. These symptoms can include: 

Dogs with severe photosensitivity will make frantic efforts to find shade or shelter due to the discomfort. 

People have been ingesting buckwheat plants in many forms, both the seeds of the plant, which do not contain fagopyrin, and the leaves, which do. The cooked seeds of the buckwheat plant are actually quite nutritious and are a gluten-free alternative to wheat and rice for dogs as well as people. The leaves of the buckwheat plant are also called buckwheat lettuce and in moderate amounts, they are a mild but tangy addition to salads and in some locales these leaves are also ground into a fine green flour and used in products like pancakes and breads. Unlike many compounds, heat does not reduce the efficiency of the toxin, however, the concentration of fagopyrin in food is unlikely to cause harm unless a very large amount is ingested or it is ingested on an ongoing basis. Buckwheat sprouts have also been added to juicing diets, but the overuse of this method of ingestion has led to cases of phototoxicity in humans as well.

The cooked seeds of the buckwheat plant are actually quite nutritious and are a gluten-free alternative to wheat and rice for dogs as well as people. The toxic compound found in the buckwheat plant is called fagopyrin and is present in all parts of the plant except the fully ripened seeds. The fagopyrin is absorbed into the bloodstream after digestion and then reacts with sunlight. The sunlight causes the fagopyrin to fluoresce and this causes radiation damage to the blood vessels. These reactions are quite often mitigated by the skin’s natural pigment, but areas of lighter skin and fur will be more likely to develop reactions, and those reactions will be more intense than areas protected by darker pigments.

The condition of the skin during the physical examination will be similar to several other types of dermal issues such as allergies, chemical damage, and flea infestations, and will usually prompt your veterinarian to get a skin scraping for cutaneous cytology.  Cutaneous cytology is the examination by microscope of harvested skin cells and will help to rule out mites, ticks, and bacterial or fungal infections that can mimic phototoxicity. The combination of photophobia and the skin reaction is strongly suggestive of some form of photosensitivity, however determining what is causing the photosensitivity can be more challenging.

If you witnessed the consumption of the plant your veterinarian will ask for more information about how much the patient ingested and how long ago the ingestion occurred, and if it was a single or repeated exposure. If the source is unknown, then the liver function will be tested to ensure that the phototoxicity isn’t due to damage to the liver or bile ducts, and questions will be asked about the animal’s usual environment to try and detect if there are any phototoxic plants such as buckwheat or St. John’s wort available for consumption.

Once the source of the phototoxicity is shown to be the buckwheat that the dog is consuming, the first course of action is to block access to the plant material. Generally, the photosensitivity will dissipate after 48 hours, but your dog should have their exposure to sunlight reduced as much as possible during that time. Sunscreen is not a suitable protectant as the fagopyrin is reacting to a different spectrum of the sunlight. Window glass is not a deterrent to this spectrum of light either, so the dog should be kept away from sunny windows and shielded from the sunlight in the car as well.

In the early stages of the reaction, corticosteroids, antihistamines, and anti-inflammatory medications may be helpful in reducing damage to the skin. In rare cases, the skin may become severely necrotic, and surgical debridement may be required. Surgical debridement is the removal of damaged or infected skin in order to allow the healthy tissue to completely heal.

Once the reaction itself has ceased, the skin condition will be re-evaluated. If the skin became necrotic or sloughed off during the course of the poisoning, it may take a few months for the skin to heal completely and for the fur to grow back in. Skin that has been damaged by phototoxicity may develop infections and either oral or topical antibiotics will be prescribed if this occurs. It is essential that your pet completes the full measure of their antibiotic medication even if the symptoms seem to have subsided. Stopping the medication before the bacteria are completely eradicated may cause the infection to reoccur.