Primary Classes of Food Allergens
The eight major food allergens responsible for approximately 90% of serious allergic reactions in the United States are: milk, egg, peanut, tree nuts, soy, wheat, fish, and crustacean shellfish. 1
The "Big Eight" Major Food Allergens
These allergens are formally recognized under the Food Allergen Labeling and Consumer Protection Act (FALCPA) and must be clearly labeled on food products: 1
In Children
- Milk - Most common pediatric allergen 1
- Egg - Frequently outgrown by school age 1
- Peanut - Often persists into adulthood 1
- Tree nuts - Typically lifelong allergy 1, 2
- Soy - More common in children, often outgrown 1
- Wheat - Usually resolves during childhood 1
- Fish - Less common in children (0.2% prevalence) 1
- Shellfish (crustacean) - Less common in children (0.5% prevalence) 1
In Adults
The pattern shifts with age, where peanuts, tree nuts, shellfish, and fish become the predominant allergens, as adults are less likely to have milk, egg, soy, or wheat allergies. 3, 2
Immunologic Classification of Food Allergens
Food allergens can be categorized by their immune mechanism: 1
IgE-Mediated Reactions
- Mechanism: Immediate hypersensitivity (Type I) targeting specific food proteins (epitopes) 1
- Timing: Symptoms occur within minutes to 2 hours after ingestion 1
- Target organs: Skin (urticaria), gastrointestinal tract, respiratory system 3
- Examples: Acute reactions to any of the major eight allergens 1
Non-IgE-Mediated Reactions
- Mechanism: T-cell mediated immunity (Type IV hypersensitivity) 1, 4
- Timing: Delayed onset, hours to days after exposure 4
- Conditions include: 1
- Food Protein-Induced Enterocolitis Syndrome (FPIES)
- Dietary protein intolerance (e.g., milk protein allergy)
- Protein enteropathy
Mixed IgE/Non-IgE Reactions
- Example: Eosinophilic esophagitis (EoE) 1
- Characteristics: Combines immediate and delayed immune mechanisms 1
Geographic and Regional Variations
While the "big eight" dominate in the United States, other regions recognize additional major allergens: 1
- European Union: Celery, mustard, sesame, lupine, and molluscan shellfish 1
- Japan: Buckwheat is considered a major allergen 1
Important Clinical Distinctions
Food Allergy vs. Food Intolerance
Food allergy is immune-mediated, whereas food intolerance involves non-immunologic mechanisms (pharmacologic, toxic, or metabolic). 1
- Lactose intolerance: Enzyme deficiency (lactase), not immune-mediated 1
- Celiac disease: Immune-mediated gastroenteropathy triggered by gluten, but not classified as a food allergy 1
Allergen Characteristics
The major food allergens share common biochemical properties: 2
- Glycoproteins that are water-soluble 2
- Heat-stable - cooking does not eliminate allergenicity 2
- Resistant to proteases and acids - survive digestion 2
- Multiple epitopes - some are homologous across related foods (e.g., peanut and tree nuts share conserved epitopes) 1
Natural History and Persistence
Children typically outgrow allergies to milk, egg, soy, and wheat, but rarely outgrow allergies to peanut, tree nuts, fish, and shellfish. 1, 2
- High initial specific IgE levels correlate with lower rates of tolerance development over time 1
- Adult-onset food allergies tend to persist and are less likely to resolve 1
- Natural tolerance can develop later than previously thought, even during adolescence 2
Clinical Pitfalls
- Sensitization is not allergy: A positive skin prick test or specific IgE without clinical symptoms does not constitute food allergy and should not prompt dietary elimination 1
- Cross-reactivity: Epitope homology means patients allergic to one tree nut may react to others, though this requires clinical confirmation 1
- Precautionary labeling (e.g., "may contain traces") is voluntary and unregulated, creating challenges for allergen avoidance 1