What Is a Tomato Allergy?

If you've ever gotten an itchy mouth or a stomachache 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.

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

Oral Allergy Syndrome (OAS)

Tomato allergy symptoms are more often than not caused by oral allergy syndrome (OAS). Also known as pollen fruit allergy syndrome (PFAS), 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 usually takes years for a cross-reaction to occur from seasonal allergies.

Food Intolderance

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 food intolerance.

Tomato Allergy Symptoms

Tru tomato allergies affect the skin, sinuses, eyes, and airways, and while rare, can cause a life-threatening reaction known as anaphylaxis.

True tomato allergy symptoms can include: 

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

OAS symptoms tend to be a milder form of food allergy. 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

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

Causes of Tomato Allergy

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. Exposure to the food allergen causes cross linking of immunoglobulin E (IgE) resulting in a cascade of reactions which release 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."

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 syndrome (IBS)-like 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 rumored to increase inflammation in autoimmune diseases, however this has not been proven in human studies. 

Tomato Allergy Treatment

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

If you have a tomato allergy and a history of anaphylaxis, your physician will prescribe a preloaded syringe of epinephrine (such as an EpiPen) to inject in the event of an emergency.

In the event of exposure and only mild reaction like oral itching or a rash, oral antihistamines like cetirizine (Zyrtec) block histamine, the chemical produced by the immune system that triggers allergy symptoms.

In cases of pollen food allergy syndrome (PFAS or OAS) to tomato, an allergist may recommend a series of allergy shots to gradually desensitize you to the true allergen (grass pollen) if you have symptoms of grass allergy. Some patients with PFAS/OAS notice improvement of symptoms to oral allergy triggers like tomato after having allergy shots to the relevant aeroallergen.

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.