What type of pollen is associated with watermelon allergy?

Pollen Associated with Watermelon Allergy

Watermelon allergy is most commonly associated with profilin, a plant pan-allergen found in various pollens, rather than with a specific pollen type. While ragweed pollen was historically thought to be specifically linked to watermelon allergy, more recent evidence indicates that profilin sensitization is the primary mechanism 1.

Pollen Cross-Reactivity Patterns

Watermelon belongs to the Cucurbitaceae family, and allergic reactions to it typically occur through cross-reactivity mechanisms involving:

Primary Cross-Reactive Pollens:

• Multiple pollen sensitizations: Patients with watermelon allergy are typically sensitized to multiple pollens rather than a single specific pollen type 1
• Weed pollens: Particularly high association with:
  • Ragweed (Ambrosia) pollen (OR 22.4) 2
  • Elm (Ulmus) pollen (OR 42.8) 2

Mechanism of Cross-Reactivity:

• Profilin: Identified as a major allergen (13 kDa protein) in watermelon, recognized by 71% of watermelon-allergic patients 3
• Other allergens: Malate dehydrogenase (36 kDa) and triose phosphate isomerase (28 kDa) have also been identified as major watermelon allergens 4

Clinical Presentation and Associations

Watermelon allergy typically manifests as:

• Oral Allergy Syndrome (OAS): The predominant clinical presentation 3
• Pollen allergy: 100% of watermelon-allergic patients also have pollen allergies 2
• Other food allergies: Particularly to:
  • Other Cucurbitaceae fruits (melon, cucumber, zucchini) 4
  • Peach (up to 62%) 2
  • Fig and kiwi 2
• Latex sensitivity: Present in up to 23% of watermelon-allergic patients 2

Diagnostic Considerations

When evaluating potential watermelon allergy:

• Look for sensitization to multiple pollens rather than a single pollen type
• Patients with sensitivity to >3 seasonal allergen sources are much more likely to react to watermelon (23%) compared to those sensitive to ≤3 seasonal allergens (1%) 1
• Skin testing with profilin-enriched extracts may be more useful than testing with specific pollen extracts 1

Pathophysiological Insights

The allergic reaction to watermelon is primarily related to:

• Profilin stability: While stable in saliva (explaining OAS symptoms), watermelon profilin is rapidly digested by pepsin in gastric fluid, which explains why systemic reactions are uncommon 3
• Cross-reactive carbohydrate determinants (CCDs): May also play a role in cross-reactivity between pollens and watermelon 5

In conclusion, watermelon allergy is primarily associated with profilin sensitization that occurs in patients with multiple pollen allergies, rather than with a specific pollen type. The most significant pollen associations are with ragweed and elm, but the cross-reactivity is mediated through shared pan-allergens rather than through specific pollen allergens.