What Is a Tomato Allergy?

A reaction to tomatoes may occur in someone allergic to grass pollen

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If you've ever gotten an itchy mouth or a stomach ache after eating a tomato, you may wonder if you have a tomato allergy. While it is possible to be allergic to tomatoes and other members of the nightshade family (like potatoes and bell peppers), it's not common.

Bowl of various tomatoes

Verywell / Zorica Lakonic

Research on tomato allergies is sparse, but one study estimated that true tomato allergies occur in about 1.5% of Northern Europeans. It is a bit more common in people from Italy (about 16% of the population).

This article discusses tomato allergies and other types of reactions from tomatoes, including oral allergy syndrome (OAS), pseudoallergies, and others. It also explains the symptoms of different types of reactions to tomatoes and how to get diagnosed.

Types of Tomato Allergies

Tomato allergies are rare. Research suggests reactions to tomatoes are more likely a sensitivity or intolerance than an actual food allergy. When a true tomato allergy occurs it is usually a type 1 hypersensitivity.

Type 1 Allergy

A true allergy to tomatoes is not very common. In a true allergy, the immune system reacts abnormally to an otherwise harmless substance (known as an allergen). This triggers allergy symptoms.

A true tomato allergy is a type 1 hypersensitivity, also known as a contact allergy. This causes reactions that can range from mild hay fever-like symptoms and hives to life-threatening anaphylaxis reactions.

Oral Allergy Syndrome (OAS)

Tomato allergy symptoms are more often than not caused by oral allergy syndrome (OAS). Also known as pollen fruit syndrome (PFS), the symptoms are caused by cross-reacting allergens.

People who are allergic to grass pollen can have an OAS reaction to tomatoes, peaches, celery, melons, or potatoes.

OAS is more common in adults and teens. Young children are usually not affected because it takes years for a cross-reaction to occur from seasonal allergies.

Pseudoallergy

Sometimes, a person has symptoms related to food but it is not a true allergy. For example, a person with sensitive skin might get irritation from the acidity of a tomato, but that does not mean that they're allergic to tomatoes. This kind of reaction is sometimes called a "pseudoallergy."

Also known as histamine intolerance, a pseudoallergy is a nonallergic hypersensitivity that mimics a true allergic reaction. Pseudoallergic reactions can be as severe as true allergies and can include anaphylaxis.

Tomato Allergy Symptoms

Type 1 allergies, OAS, and pseudoallergies affect the skin, sinuses, eyes, and airways, and while rare, can cause a life-threatening reaction known as anaphylaxis.

Type 1 tomato allergy and pseudoallergy symptoms can include: 

  • Congestion, runny nose, and sneezing
  • Red eyes
  • Hives
  • Rashes
  • Swelling
  • Asthma

OAS symptoms tend to be milder than type 1 allergy symptoms. The reactions tend to be brief (a few seconds or minutes) and include:

  • A slight itching, burning, or tingling sensation
  • Mild swelling of the lips, mouth, tongue
  • Transient nasal congestion, sneezing, or nasal drip

OAS symptoms are more likely to occur when the seasonal pollen count is high. Though rare, OAS can also cause anaphylaxis.

When to Seek Emergency Care

Anaphylaxis is a potentially life-threatening reaction where the throat and airways swell up.

Seek medical care right away if you experience any of the following smptoms:

  • Trouble breathing
  • Hives
  • Facial swelling
  • Rapid heart rate
  • Confusion
  • Dizziness
  • Fainting
  • Confusion

Causes

A true tomato allergy is caused by an immune system response known as a type 1 hypersensitivity. A type 1 hypersensitivity causes an immediate reaction to an allergen. The immune system releases immunoglobulin E (IgE) resulting in a cascade of reactions causing the release of histamine.

OAS reactions to tomatoes are caused by an allergy to grass pollen that cross-reacts with tomatoes. Both contain proteins known as profilins. While not identical, the profilins are close enough to potentially trigger an allergic response.

Pollen allergies are seasonal. The body responds stronger with each passing season. Over time, the immune system can start to react to substances with similar proteins, such as fruits, vegetables, spices, or nuts.

A pseudoallergy is caused by a histamine reaction and has similar symptoms to a true allergy. The main difference is the presence of IgE. A true allergy begins with an IgE reaction, whereas a pseudoallergy does not.

Precisely what causes a pseudoallergy is unclear and there is some dispute in the medical community as to the validity of the term.

Diagnosing Tomato Allergies

Getting diagnosed with a true tomato allergy or OAS related to tomatoes involves working with your provider and an allergist. An allergist can identify the specific allergens you are sensitive to. There are a variety of allergy tests that can be used, including:

  • Blood tests to detect specific allergen antibodies
  • Skin-prick tests in which the allergen is inserted into the skin with a tiny scratch
  • Oral challenges in which food is eaten slowly, in gradually increasing amounts, to assess the allergic response

What Else Can Cause A Reaction to Tomatoes?

Some people may have reactions to tomatoes that are not actual tomato allergies.

FODMAP Intolerance

Fructans in tomatoes can cause uncomfortable digestive symptoms in people sensitive to FODMAPs. FODMAP stands for:

  • Fermentable
  • Oligosaccharides (comprised of fructans and galactans)
  • Disaccharides (milk sugar lactose)
  • Monosaccharides (fructose)
  • And
  • Polyols (sugar alcohols such as sorbitol, mannitol, xylitol, and maltitol)

Several different fruits, vegetables, and grains are classified as FODMAPs. Tomatoes are a low FODMAP food when eaten in small quantities. However, large servings of tomato products—like tomato sauce—can cause an inflammatory bowel disease (IBD) reaction.

Nightshade Sensitivities

Some people who seem to react to tomatoes find they are actually sensitive to nightshades. Common nightshades include tomatoes, potatoes, peppers, eggplants, blueberries, tomatillos, and paprika.

A sensitivity to nightshades can be an allergic reaction, oral allergy syndrome, or intolerance. A nightshade sensitivity or intolerance commonly causes heartburn, gas, bloating, nausea, vomiting, and diarrhea.

Nightshades are also rumored to increase inflammation in autoimmune diseases. However, the only condition where this has been proven is inflammatory bowel disease. 

Tomato Allergy Treatment

The treatment for a tomato allergy, OAS, and pseudoallergies is more or less the same: Avoid tomatoes.

In the event of exposure, oral antihistamines like Benedryl (diphenhydramine) block histamine, the chemical produced by the immune system that triggers allergy symptoms.

If the allergy is severe, an allergist may recommend a series of allergy shots to gradually desensitize you to the true allergen (grass pollen) as well as the food allergen (tomato).


If you have a tomato allergy and a history of anaphylaxis, you may need to carry a preloaded syringe of epinephrine (such as an EpiPen) to inject in an emergency.

Summary

It's not common, but it is possible to be allergic to tomatoes. However, most people who have symptoms when they eat a tomato probably have an intolerance to the food rather than a true allergy.

If you have other allergies, especially grass pollen allergies, you're more likely also to have an allergic reaction to tomatoes. It's rare, but some people with severe allergies may have anaphylaxis—a potentially life-threatening reaction.

Frequently Asked Questions

  • How rare is a tomato allergy?

    Research on tomato allergies is limited, but one study found that about 1.5% of Northern Europeans are truly allergic to tomatoes. The allergy is a little more common in people from Italy, where about 16% of the population has it.

  • Is it possible to be allergic to tomatoes but not ketchup?

    If you have a true allergy to tomatoes, you need to avoid all products made with tomatoes—including ketchup. However, if you have a tomato food intolerance rather than an allergy, you might not have a problem with ketchup.

  • Will cooked tomatoes cause an allergic reaction?

    Maybe, maybe not. In a tomato allergy or OAS, the immune system typically reacts to the profilins in raw tomato. Cooking or baking the fruit may break down these proteins and render them harmless.

    However, if you have ever had a serious allergic reaction to tomatoes you may not want to risk it.

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By Daniel More, MD
Daniel More, MD, is a board-certified allergist and clinical immunologist. He is an assistant clinical professor at the University of California, San Francisco School of Medicine and currently practices at Central Coast Allergy and Asthma in Salinas, California.