# Pollen-Food Allergy Syndrome: Allergens, Clinical Insights, Diagnostic and Therapeutic Challenges
## 7 PFAS Diagnosis
### Skin Prick Testing (SPT)  
Skin trick testing (SPT) is a key diagnostic tool for identifying immunoglobulin E (IgE)-mediated allergic reactions, including PFAS [98]. SPT provides a reliable, minimally invasive method to confirm sensitization to specific pollens and foods in patients presenting with symptoms like oral itching, swelling, or systemic reactions following ingestion of certain foods [189]. The technique is particularly valuable in PFAS cases because it can identify the primary pollen allergen responsible for cross-reactivity and assess the patient's risk profile for food allergens. The European Academy of Allergy and Clinical Immunology (EAACI) strongly recommends skin prick testing and/or serum-specific IgE measurement as first-line diagnostic tools for patients with a history suggestive of IgE-mediated food allergy [98]. Figure 4: PFAS diagnosis flowchart. The flowchart illustrates a structured approach for clinicians to evaluate and confirm the diagnosis of pollen–food allergy syndrome (PFAS). SPT involves introducing a small amount of allergen extract into the superficial layers of the skin, typically on the forearm or back, using a sterile lancet. The procedure begins with the application of control solutions: a positive control (histamine) to confirm the skin's reactivity and a negative control (saline or glycerin) to rule out non-specific skin irritation. Allergen extracts from relevant pollens (e.g., birch, grass, ragweed) and foods (e.g., apple, peach, hazelnut) are then applied in separate spots. After 15-20 min, the wheel and flare are measured. A positive result is indicated by a wheel diameter of at least 3 mm larger than the negative control [189; 190]. In PFAS, SPT often reveals sensitization to pollens with corresponding reactions to related food extracts, confirming the cross-reactivity underlying the syndrome [191]. In PFAS diagnosis, commercial food extracts used in SPT may not always contain the heat-labile proteins responsible for allergic reactions, such as PR-10 proteins or profiling [192; 193]. These proteins are easily degraded during food processing and storage, making the extracts less reliable for identifying food-related allergies. To address this limitation, fresh food testing, also known as the \"prick-to-prick\" method, is commonly employed. In this technique, a sterile lancet is first pricked into a piece of the suspected fresh food (e.g., raw apple or peach) and then applied to the patient's skin [187]. Fresh food testing is particularly effective for detecting PFAS-related allergens, as it ensures that the relevant proteins remain intact and available for testing [192]. This method complements testing with commercial extracts and improves diagnostic accuracy, especially in cases where patients report symptoms but commercial extracts yield negative results [187]. SPT results for PFAS must be interpreted carefully to differentiate between primary food allergies and cross-reactive sensitivities. For example, a positive test to birch pollen (Bet v 1) accompanied by reactions to apple, carrot, or hazelnut suggests PFAS rather than a primary food allergy. Similarly, sensitization to grass pollen (Phl p 12) with reactions to melon or tomato points to profilin cross-reactivity. Conversely, strong reactions to specific foods without associated pollen sensitization may indicate a primary food allergy unrelated to PFAS. In some cases, component-resolved diagnostics (CRD) may be used alongside SPT to measure specific IgE to individual allergenic proteins, such as Bet v 1 (birch), Mal d 1 (apple), or Api g 1 (celery). This approach provides detailed insights into the cross-reactivity mechanisms driving PFAS and helps tailor management strategies [98]. The strengths and limitations of skin prick testing (SPT) are summarized in Table 2, providing a clear comparison of its advantages and challenges in diagnosing PFAS.