What Is Watermelon Allergy?

Watermelon allergy symptoms are usually different from those caused by a typical food allergy. An allergic reaction to watermelon includes symptoms of oral allergy syndrome (OAS), also known as pollen food allergy syndrome (PFAS).

OAS symptoms are caused by allergens found in both pollen and raw fruit, vegetables, and some nuts. If you are allergic to a specific type of pollen, for example, you may be allergic to foods that contain a comparable allergen. This is called cross-reactivity.

This article explains watermelon allergy symptoms, diagnosis, and treatment. It also covers risk factors for developing a watermelon allergy and which foods to avoid if you develop OAS.

Symptoms of Watermelon Allergy

Unlike food allergies, which can cause systemic (body-wide) symptoms, watermelon allergy caused by OAS usually only produces localized itching and swelling. Symptoms of OAS include:

• Itchy mouth
• Scratchy throat
• Lips, mouth, tongue, throat swelling

People with OAS usually only experience a reaction when eating raw fruits or vegetables because cooking alters the proteins involved. These symptoms typically begin immediately after putting the watermelon in your mouth and go away soon after swallowing it.

Risk Factors for Watermelon Allergy

A ragweed allergy is associated with OAS reactions to watermelons. Though anyone can develop OAS, the condition is less common in young children.

What Causes Watermelon Allergy?

Certain foods correlate with particular environmental allergens. For example, if you are allergic to various types of melons, you may also experience allergic rhinitis (nasal allergies) caused by ragweed pollen.

OAS symptoms are your body reacting to the proteins in the fruit that resemble those in pollen. This cross-reactivity confuses the immune system, resulting in OAS symptoms.

Other common correlations include the following.

• Birch pollen: apple, almond, carrot, celery, cherry, hazelnut, kiwi, peach, pear, plum
• Grass pollen: celery, melons, oranges, peaches, tomato
• Ragweed pollen: banana, cucumber, melons, sunflower seeds, zucchini

While the above associations are possible, they do not exist for everyone. For example, a person with birch pollen allergy may have OAS when eating apples but not react to any other foods associated with birch pollen. Similarly, a person may have a ragweed pollen allergy and only notice oral symptoms with melons.

Watermelon Allergy in Children and Babies

A 2015 study published in the International Dental Journal evaluated the prevalence of OAS in children. In 120 kids with seasonal allergic rhinitis, OAS symptoms were most pronounced in those with a birch allergy.

In addition, OAS was more common in teens than older children and more prevalent in those with allergic rhinitis and asthma, and allergic rhinitis and eczema.

In some cases, a person may not experience an allergic reaction to watermelon for years, but suddenly develop OAS later in life.

How is Watermelon Allergy Diagnosed?

A careful history can usually provide enough clues to a healthcare provider that watermelon is the culprit. However, some diagnostic tools can help them confirm it.

Allergy testing may include:

• A skin test, in which an allergist (an allergy specialist) scratches your skin with an allergen and watches for a reaction
• A blood test, in which a lab technician evaluates your blood for IgE antibodies. Levels of these antibodies rise in people with allergies.
• An oral food challenge, in which you consume foods you might be allergic to and document any reaction

In oral allergy syndrome to watermelon (pollen food allergy syndrome), watermelon allergy tests can be negative.

When to See a Healthcare Provider

Because the symptoms are mild and fade quickly, treatment is not usually necessary in people with a watermelon allergy.

Still, if you experience symptoms of OAS, it's a good idea to make an appointment with an allergist or your primary healthcare provider for a diagnosis. 

However, if you experience symptoms of anaphylaxis, like difficulty breathing, swelling, or hives, seek emergency medical care immediately.

To avoid another severe reaction, a healthcare provider will likely prescribe an EpiPen. An EpiPen is an injectable device that contains a synthetic form of the hormone epinephrine. Injecting the hormone can stop the reaction and give you time to seek emergency medical care.

Foods to Avoid

If you have a watermelon allergy, avoid consuming watermelon. In addition to whole watermelon, keep an eye out for watermelon in salads, drinks, and smoothies.

People with OAS often have reactions to more than one food. If you have a ragweed allergy, you may also react when you eat these foods:

• Banana
• Cantelope
• Chamomile
• Cucumber
• Echinacea
• Honeydew
• Sunflower seeds
• Zucchini

If you notice a reaction to these or any other foods, add them to your list of foods to avoid.

Summary

In some people, eating watermelon can trigger oral allergy syndrome. If you have an allergy to a specific type of pollen, a specific protein in watermelon can trigger the same type of reaction. This is called cross-reactivity.

Symptoms are immediate and localized and include itching and tingling in the mouth and throat. They usually resolve quickly once you've swallowed the fruit. Rarely, anaphylaxis can occur. Avoiding watermelon prevents a reaction. For severe reactions, using an EpiPen and getting emergency medical attention is key.