If you have an allergic reaction to tomatoes, does that mean you’re allergic to all tomato-based products — like ketchup or pasta sauce? Many MyFoodAllergyTeam members avoid anything with tomato due to a tomato allergy. “I am still missing all things tomato, even though it’s been over five years since it was added to my allergy list,” shared one member.

However, for some people, tomato products like ketchup don’t cause any problems, while raw tomatoes do. If this rings true for you, you might have oral allergy syndrome (OAS). An allergic reaction to tomatoes may be a sign of allergies to other foods or products too.

Read on to learn more about what causes an allergic reaction to tomatoes but not ketchup or other tomato products, what the symptoms are, and what to do about a tomato allergy.

Oral Allergy Syndrome Can Cause an Allergic Reaction to Certain Foods

Oral allergy syndrome, also called “pollen-food allergy syndrome,” occurs when an allergy to a certain grass, weed, or tree pollen causes allergy symptoms after eating related fruits or vegetables. The proteins in these fruits or vegetables are similar to those in the pollen, which can confuse the immune system and make the body have an allergic reaction. This is called “cross-reactivity.”

Oral allergy syndrome is a type of contact allergic reaction that happens when the raw fruit or vegetable touches your mouth or throat.

Health experts estimate that up to 1 out of 3 people with pollen allergies may experience OAS, though the numbers may be higher since it’s often undiagnosed.

Tomatoes Can Cause Oral Allergy Syndrome

Tomatoes are one of the foods that cause oral allergy syndrome because some of their proteins resemble those found in grass and birch pollen. Therefore, if you have grass or birch pollen allergies and you eat a tomato, your body thinks it’s coming in contact with that pollen, and the immune system will mount an allergic reaction.

Tomato Products May Not Cause an Allergic Reaction

An allergic reaction due to oral allergy syndrome usually occurs only with fresh fruits and vegetables, not cooked or processed forms. For example, you may have an allergic reaction to cucumbers but not pickles. This is because the proteins in the food are changed when they’re heated up or otherwise processed. After they’re cooked, the immune system doesn’t recognize them as a threat.

This is why you might have an allergic reaction to tomatoes but not ketchup. You might also be able to eat canned tomato products without any problems but not fresh tomatoes. The tomato proteins that look like grass or birch pollen change during processing. The body then doesn’t sense a threat when you eat cooked, tomato-based foods like ketchup or tomato sauce.

Symptoms of Oral Allergy Syndrome Are Usually Mild

Oral allergy symptoms are usually mild. The most common symptom is itchiness or a tingling sensation in the mouth or throat. Other symptoms may include:

• Sore or scratchy throat
• Itchy nose or ears
• Hoarseness
• Discoloration or swelling of the lips or face

OAS symptoms usually appear right away, within minutes of eating the responsible food. They can last from a few minutes to half an hour. Sometimes symptoms affect areas other than the face, mouth, or throat, but this is rare. Severe allergic reactions, such as anaphylactic shock, are also rare.

Because the symptoms are often mild and short, treatment is usually not needed. However, for people with more severe reactions, a doctor may recommend allergy medications, such as an epinephrine auto-injector or allergy shots.

An Allergic Reaction to Tomatoes May Be Seasonal

Some people with OAS have allergy symptoms only during pollen season and are able to eat the raw fruits or vegetables that would normally cause problems other times of the year. For example, you might experience a reaction to tomatoes only when your pollen allergies are acting up.

It’s Best To Talk to a Doctor About Tomato Allergies

Tell your doctor or allergist about your symptoms when you eat tomatoes or other foods. Even though OAS symptoms may be mild, they can be a sign of a more serious allergy, such as a latex allergy. It may be safest to avoid all forms, cooked or raw, of the foods that signal an allergic reaction for you.

To help you stay comfortable and safe, your doctor may do an allergy test to figure out if you have allergies to other foods or products. They can also help determine your risk of a more serious reaction, such as anaphylaxis.

Talk With Others Who Understand

On MyFoodAllergyTeam, people share their experiences with food allergies, get advice, and find support from others who understand.

Do you have an allergic reaction to tomatoes but not ketchup? Do you have other food allergies or pollen allergies? Let others know in the comments below.