Food Allergy

1. History taking (The most critical component for making an accurate diagnosis)

• When symptoms appear later or are more variable, identifying the causative food becomes more difficult. 
• The suspected food, its preparation, the amount consumed, the time interval between ingestion and symptom onset, the nature and severity of the symptoms, the number and consistency of reactions, and the presence of cofactors such as exercise, aspirin, or alcohol.

2. Physical examination

• Malnutrition, or failure to thrive

3. Skin test

• Skin prick tests using food allergens are useful for identifying the causative foods of immediate-type hypersensitivity reactions, although results may be affected by factors such as the use of antihistamines and the examiner’s level of experience. 
• For fruits and vegetables, which are less stable than animal proteins, commercial extracts may lead to false-negative results. In such cases, performing a prick-to-prick test—using a lancet to puncture the fresh food and then applying it directly to the skin—can improve diagnostic accuracy.

4. Laboratory Testing

 4-1. Allergen-Specific IgE Antibodies

• Multiple allergen simultaneous test (MAST): More meaningful as a qualitative test 
• ImmunoCAP: The quantitatively measure specific IgE antibodies and is a highly specific, sensitive, and reproducible test. For certain foods, the diagnostic decision point of food-specific IgE levels measured via ImmunoCAP can aid in diagnosing food allergy without the need for food challenge testing.
• The measurement of food-specific IgG or IgG4 antibodies is not scientifically validated and is not useful for the diagnosis of food allergy.

4-2. Component-Resolved Diagnosis

• Measurement of IgE responses to individual allergenic proteins: Distinguishing between true sensitization to a specific food and cross-reactivity, predicting clinical manifestations and determining prognosis.

5. Oral food challenges (OFCs): The gold standard for diagnosing food allergies

• Double-blind, placebo-controlled food challenges (DBPCFCs) are used primarily in research, while open or single-blind challenges are more common in clinical practice. 
• The procedure involves gradual dosing in a medical setting with emergency support available. Proper patient selection, informed consent, and medication review are essential beforehand. 

1. Trigger-food avoidance

 1-1. Principles of trigger-food avoidance (The classic treatment approach)

• Effective avoidance must consider not only foods containing the allergen as a main ingredient, but also condiments, sauces, supplements, cross-reactive foods, shared cooking utensils, and contamination during food preparation. 
• Over-restrictive avoidance can reduce dietary diversity, impair quality of life for the patient and family, cause social or psychological distress, and lead to nutritional deficiencies.
• In infants with milk allergy, breastfeeding is recommended when possible; if not feasible, hypoallergenic formulas (either extensively hydrolyzed or amino acid–based) are recommended. 
• Packaged foods should be checked for allergen labeling.

 1-2. Heat-treated milk and egg

• Consumption of such high heat–treated milk or egg products may be permitted if tolerated.

 1-3. Nutritional management during elimination diets

• Nutrition counseling, especially when the patient has multiple food allergies, growth delay, or calcium/vitamin D deficiency. 
• Periodic reassessment is important to determine if the allergy has resolved naturally

2. Treatment of acute symptoms

• Antihistamines
• Bronchodilators
• Systemic corticosteroids
• Intramuscular epinephrine

3. Immunotherapy

• Because food allergies increasingly persist beyond the expected age of resolution, active immunotherapy to induce immune tolerance is receiving greater attention in patients for whom natural resolution is unlikely. Various routes exist—oral, epicutaneous, sublingual, or subcutaneous—but oral immunotherapy (OIT) is most commonly used in clinical practice.
• OIT induces desensitization in most patients and, in some cases, sustained tolerance, although adverse reaction rates are relatively high. OIT is used for milk, egg, and peanut allergy to increase reaction thresholds or induce lasting tolerance. It is recommended to begin in children who still have allergies at around 4–5 years old, starting with a small safe dose determined by prior oral food challenge, gradually escalating, and maintaining for years.

4. Biologic agents

• Biologics targeting IgE or key cytokines can be used alone or alongside OIT to reduce adverse reactions and shorten the initial phase. Omalizumab (anti-IgE) may be used for this purpose, and newer biologics such as dupilumab, ligelizumab, and mepolizumab are currently under investigation.

5. Patient and caregiver participation

• Education: Trigger-food avoidance, individualized management plans, recognition of anaphylaxis, and emergency preparedness including self-injectable epinephrine use.  
• Shared decision-making tools and multidisciplinary integrated care 

6. Eosinophilic gastrointestinal disease, non-IgE mediated food allergy

6-1. Eosinophilic gastroenteritis

• If a food shows a positive reaction on allergy testing performed alongside clinical history, that food should be eliminated. 
• If allergy testing does not help identify the cause, an empiric six-food elimination diet (typically excluding milk, soy, egg, wheat, nuts, and seafood) may be implemented. 
• After eliminating specific foods from the diet for at least 6–8 weeks, patients undergo repeat endoscopy to reassess histopathologic changes. 
• If improvement is noted, foods are reintroduced one at a time, with follow-up endoscopies to identify specific food triggers. 
• If eosinophil counts do not improve during follow-up, further dietary restrictions may be necessary. 
• In severe cases: Elemental diet, proton pump inhibitors, montelukast, ketotifen, and systemic steroids may also be considered.

6-2. In non-IgE-mediated food allergy 

• The offending food should be eliminated for a certain period
• When the child reaches an age at which improvement is expected, an oral food challenge may be performed to reassess tolerance and resume dietary intake. 
• For acute symptoms, supportive treatments(adequate fluid replacement, antiemetics, and intravenous corticosteroids)