Food Allergy

Food allergy is an immune-mediated adverse reaction to food that includes both IgE-mediated and non-IgE-mediated responses. It results from a failure to establish immune tolerance to ingested food, leading to a Th2-skewed immune response, although the exact mechanisms underlying its initiation and promotion remain unclear. Sensitization to food antigens can occur through the skin, gastrointestinal tract, or respiratory tract. Allergic reactions may manifest via IgE-mediated, non-IgE-mediated, or mixed mechanisms, affecting the skin, gastrointestinal tract, respiratory system, and cardiovascular system.

Adverse food reactions

  Immune mediated

• IgE mediated 
• Mixed IgE and non-IgE: Eosinophilic gastrointestinal disease (EGID)
• Non-IgE mediated: Food protein induced enteropathy, celiac disease
• Cell mediated: Allergic contact dermatitis

  Non-immune mediated

• Metabolic: Lactose intolerance
• Pharmacologic
• Toxic
• Other

1. IgE-Mediated Symptoms

These reactions typically occur within minutes to 2 hours after allergen exposure.

 1-1. Cutaneous Symptoms

• Urticaria
• Atopic dermatitis

1-2. Respiratory Symptoms

• Nasal itching, congestion, sneezing, cough, dyspnea, and wheezing
• A sudden, staccato cough (laryngeal obstruction.)

1-3. Gastrointestinal Symptoms

• Nausea, abdominal pain, vomiting, and diarrhea

1-4. Pollen-Food Allergy Syndrome (Oral Allergy Syndrome)

• - Itching or mild swelling in the mouth/throat after eating raw fruits, vegetables, or certain nuts. 

1-5. Cardiovascular Symptoms

• In child, food-induced cardiovascular reactions typically follow respiratory symptoms. In contrast, adults may experience sudden cardiovascular collapse as the first sign. 
• Shock and hypotension 

1-6. Anaphylaxis

2. Non–Immunoglobulin E Immune-Mediated Reactions to Food

 2-1. Celiac Disease

• An autoimmune disorder where antibodies against gluten damage intestinal epithelial cells. Symptoms resolve with a gluten-free diet. Nearly all patients have HLA-DQ2 or DQ8 haplotypes. Dermatitis herpetiformis may co-occur and mimic atopic dermatitis.

2-2. Eosinophilic Gastrointestinal Disorders (e.g., Eosinophilic Esophagitis)

• Nausea, vomiting, abdominal pain, hematochezia or melena, malabsorption

2-3. Food Protein–Induced Enterocolitis Syndrome (FPIES)

• Repetitive vomiting around 2 hours after food ingestion, often with pallor and hypotension in severe cases. Unlike IgE-mediated allergies, recovery is not immediate and vomiting is prolonged. 

2-4. Food Protein–Induced Proctocolitis

• Bloody stools in otherwise healthy infants

1. Maternal Diet During Pregnancy and Lactation

• There is no evidence to support restricting specific foods during pregnancy or lactation to prevent food allergies in infants, including those at high risk for allergic diseases.
• If an exclusively breastfed infant develops immediate-type food allergic symptoms in response to maternal consumption of a particular food, or if there is suspected association with maternal diet in infants with atopic dermatitis, and a specific food is confirmed as the cause, it is appropriate to eliminate that food from the maternal diet during breastfeeding.

2. Breastfeeding and Infant Formula

• Exclusive breastfeeding is recommended for all infants, including those at high risk for allergic diseases, during the first 4–6 months of life. 
• In high-risk infants who require formula feeding before 4 months of age, the use of extensively or partially hydrolyzed formula may be effective in preventing food allergy 

3. Complementary Feeding and Introduction of Major Allergens

• Complementary feeding should begin between 4 to 6 months of age, regardless of allergy risk status, and no specific food should be excluded from the weaning diet without medical indication. 
• Acidic fruits (e.g., strawberries, berries, tomatoes, citrus fruits) may cause perioral rashes due to acid irritation and high histamine content 
• Fresh cow’s milk should not be given before 1 year of age due to renal load and low iron content. 

In infants fed with formula from early weeks of life, regular early introduction of peanut and egg during the weaning period has been reported to help prevent food allergy to these items.