Although tomatoes are one of the most-consumed vegetables in the Western diet, allergies to tomatoes are very rare. However, if you can't digest tomatoes, or if you experience intestinal upsets after eating them, you may have a more common tomato intolerance that can result from several causes.
Tomato Intolerance or Allergy?
If eating tomatoes gives you symptoms of indigestion, or worse, you may have a hypersensitivity, such as tomato intolerance, or a food allergy. A tomato intolerance can often cause some similar symptoms as a tomato allergy, so it's important to see an allergist. They may give you a scratch test, or a blood test that can identify the cause of your reaction to eating tomatoes.
A food allergy is an abnormal immune response to a protein in a food. A food intolerance, or sensitivity, is a non-immunological response initiated by a food or food component at a dose normally tolerated, as defined by a review in Nutrients, published in July 2019.
If you have been diagnosed with an allergy to tomatoes, you may also be allergic to other members of the nightshade group, which includes potatoes and eggplants. In addition, you may have a cross-reaction to birch pollen and latex, called latex-fruit syndrome. The immune system may recognize these pollens and proteins as antigens, and direct an allergic response against them, causing side effects.
Adverse reactions to foods can vary with individuals. An immune system response to tomatoes can cause symptoms far beyond digestive problems. According to DailyMed these can include:
- Joint pain
- Stiffness
- Headaches
- Dizziness
- Diarrhea
- Mild depression
- Nausea
- Skin irritations
Severe allergies to tomatoes are rare, but, as with any allergy, reactions can be life-threatening; they may require immediate medical attention.
The American Academy of Family Physicians says that allergic reactions are often caused by raw foods only; cooking may distort the protein allergens so that the immune system does not recognize them as a foreign substance. Some people find that they can tolerate ketchup, spaghetti sauce and pizza without any adverse effects.
What’s a Tomato Sensitivity?
While people with food allergies are generally advised to completely avoid offending foods, food intolerances are often dose-related. If you have a tomato intolerance, you may not have symptoms unless you eat a large amount, or eat tomatoes frequently, says the Cleveland Clinic. With a tomato sensitivity or intolerance, symptoms are generally not severe and primarily include digestive disorders. Some of these may include:
- Nausea
- Stomach pain
- Gas, cramps or bloating
- Vomiting
- Heartburn
- Diarrhea
- Headaches
- Irritability or nervousness
There are several underlying causes that could occasion a sensitivity to tomatoes with reactions resulting in gastric discomfort, according to the Mayo Clinic. These include:
- Absence of an enzyme in your body that is needed
to properly digest certain proteins in food.
- Chronic medical conditions, such as irritable
bowel syndrome, that make you more sensitive to some foods.
- Sensitivity to food additives that provide color, enhance taste or inhibit bacteria in canned,
processed or dried tomatoes — for
example, sulfites used to preserve dried tomatoes.
- Psychological avoidance, often caused by recurring stress. Sometimes the mere thought of a food may make you feel sick. The reason is not fully understood.
Other Causes of Digestive Problems
Intestinal complaints from eating tomatoes may also come from a histamine–induced response. Tomatoes, including tomato juice and ketchup, are rich in histamines, according to the 2019 article in Nutrients. Histamines are compounds that activate the immune system's signals to attack external threats.
Certain conditions may cause a lack of the enzymes that your body needs to break down histamines from foods. Excess histamines can enter the bloodstream, which can initiate an immune response. Being high in histamines, tomatoes can contribute to an accumulation and overload, and cause undesirable symptoms. According to the review in Nutrients, these may include:
- Nausea
- Vomiting
- Diarrhea
- Abdominal pain
For some people, especially those suffering from gastroesophageal reflux disease (GERD), the high acid content of tomatoes and tomato-based products can contribute to gastrointestinal irritation, including reflux, indigestion and heartburn. Heartburn, also known as acid indigestion, occurs when food and stomach acids back up into the esophagus, causing an uncomfortable burning feeling in the chest. UC Davis Health suggests eliminating tomatoes from your diet to reduce reflux.
Another cause of digestive problems after eating tomatoes is bacteria. Raw tomatoes are susceptible to salmonella contamination, as reported in a study published in the International Journal of Food Microbiology in March 2019. Imported tomatoes may be hydrated in the field, or washed during processing, with water contaminated with the bacteria.
Salmonella infection can affect the intestinal tract and, if you have a sensitivity to tomatoes, you may be at higher risk for symptoms. Symptoms can include diarrhea, fever and abdominal cramps, according to the Mayo Clinic.
- PlosOne: "Effect of Tomato Variety, Cultivation, Climate and Processing on Sola l 4, an Allergen from Solanum Lycopersicum"
- Division of Medical Devices: "Latex-Fruit Syndrome and Class 2 Food Allergy"
- DailyMed: "Allergies Nightshades"
- American Academy of Family Physicians: "Food Allergies"
- Cleveland Clinic: "Food Problems: Is it an Allergy or Intolerance"
- Mayo Clinic: "Food Allergy vs. Food Intolerance: What's the Difference?"
- UC Davis Health: "Quenching the Fire of Heartburn"
- International Journal of Food Microbiology: "Control of Salmonella Newport on Cherry Tomato Using a Cocktail of Lytic Bacteriophages"
- Mayo Clinic: "Salmonella Infection"