How Your Tomato Allergy May Be Caused by Grass Pollen

Bowl of various tomatoes

Verywell / Zorica Lakonic

While people can develop allergies to any number of foods they eat, there may be times when they are not considered to be a true food allergy. A true allergy is one in which the immune system will react abnormally to an otherwise harmless substance (known as an allergen) and trigger allergy symptoms.

There is another form of allergy, referred to as oral allergy syndrome (OAS), in which the symptoms are caused by cross-reacting allergens. With OAS, a person with a true pollen allergy will often become sensitive to foods that have a similar protein structure.

A tomato is a prime example of this. Someone who has a grass pollen allergy might also become sensitive to tomatoes because they both contain profiling, a type of protein. While the profilins in tomatoes are not identical to those in pollen, they are close enough to potentially trigger an allergic response.

OAS and Tomatoes

When due to OAS, the tomato allergy is not considered the true allergy because it is a consequence of the grass pollen allergy. A person with a grass pollen allergy will likely have a tomato allergy, but not the other way around. OAS tends to be a one-way street in which the pollen is the true allergy.

The reason for this is that pollen allergies are seasonal, and the body tends to respond to them more rapidly and robustly with each passing season. With time, the immune system can become increasingly sensitive to other substances (such as fruits, vegetables, spices, or nuts) that contain similar protein structures.

This is why OAS doesn't usually affect young children. It develops more commonly in teens and young adults, even if they have been eating certain fruits or vegetables for years without problems. As the body becomes increasingly responsive to seasonal allergies, triggered year after year, the symptoms of OAS will begin to develop.

In addition to tomatoes, someone with a grass pollen allergy may also develop sensitivities to peaches, celery, melons, or potatoes.

Symptoms

Because the proteins in tomato are slightly different from those in grass pollen, the symptoms of OAS tends to be milder and may include:

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

Symptoms of OAS usually only last for a few seconds or minutes and rarely progress to anything more serious. They are also more likely to occur when the seasonal pollen count is high.

Moreover, because the immune system is reacting the profilins found in raw tomato, cooking or baking the fruit will break down these proteins and render them harmless. This is why some people can tolerate tomato or peach sauce but not fresh tomato or peach.

In rare cases, a person with OAS may experience a more extreme allergic response known as anaphylaxis. This would usually only happen in persons with severe grass-pollen allergies. Symptoms of anaphylaxis include respiratory distress, hives, facial swelling, rapid heart rate, confusion, dizziness, facial swelling, fainting, and confusion.

Anaphylaxis is considered a medical emergency. If left untreated, it can lead to coma, shock, cardiac or respiratory failure, and even death.

Diagnosis

If you have severe or worsening allergy symptoms, you may need to ask your doctor for a referral to an allergist who can help identify the specifics allergens you are sensitive to. There are a variety of tests that can use, 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

Treatment

For persons with confirmed OAS, avoidance of the food triggers is advised, especially during allergy season. If the allergy is severe, the allergist may recommend a series of allergy shots to gradually desensitize you to the true allergen (grass pollen) as well as the food allergen.

In the event of exposure, oral antihistamines can provide relief by blocking histamine, the chemical produced by the immune system that triggers allergy symptoms.

Persons with a history of anaphylaxis may need to carry a preloaded syringe of epinephrine (such as an EpiPen) to inject in the event of an emergency.

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  2. Gill, Parwinder et al. Anaphylactic Shock in Oral Allergy. The Journal of Allergy and Clinical Immunology. doi:10.1016/j.jaci.2012.12.1439