Food Allergens and Their Characteristics

Introduction to Major 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, as recognized by the Food Allergen Labeling and Consumer Protection Act (FALCPA) 1, 2, 3
These allergens must be clearly labeled on food products, according to the FALCPA guidelines 3

In children, milk is the most common pediatric allergen, while egg is frequently outgrown by school age 1, 4, 5
Peanut allergy often persists into adulthood, and tree nuts typically represent a lifelong allergy 4, 6
Soy allergy is more common in children and is often outgrown, whereas wheat allergy usually resolves during childhood 1, 2, 7
Fish and shellfish (crustacean) allergies are less common in children, with a prevalence of 0.2% and 0.5%, respectively 6

Food allergens can be categorized by their immune mechanism, including IgE-mediated reactions, non-IgE-mediated reactions, and mixed IgE/non-IgE reactions 1, 7, 8
IgE-mediated reactions involve immediate hypersensitivity (Type I) targeting specific food proteins (epitopes), with symptoms occurring within minutes to 2 hours after ingestion 1, 5, 7
Non-IgE-mediated reactions involve T-cell mediated immunity (Type IV hypersensitivity) with a delayed onset, hours to days after exposure, and include conditions such as Food Protein-Induced Enterocolitis Syndrome (FPIES) and dietary protein intolerance 1, 7, 9

The "big eight" major food allergens dominate in the United States, but other regions recognize additional major allergens, such as celery, mustard, sesame, lupine, and molluscan shellfish in the European Union, and buckwheat in Japan 10

Food allergy is immune-mediated, whereas food intolerance involves non-immunologic mechanisms, and it is essential to distinguish between the two to provide appropriate management and treatment 2, 4
Lactose intolerance is an example of a non-immune-mediated condition, resulting from an enzyme deficiency (lactase), whereas celiac disease is an immune-mediated gastroenteropathy triggered by gluten, but not classified as a food allergy 1, 2, 4, 7

Children typically outgrow allergies to milk, egg, soy, and wheat, but rarely outgrow allergies to peanut, tree nuts, fish, and shellfish, with high initial specific IgE levels correlating with lower rates of tolerance development over time 6
Adult-onset food allergies tend to persist and are less likely to resolve, emphasizing the need for continued vigilance and management 6

Sensitization is not equivalent to allergy, and a positive skin prick test or specific IgE without clinical symptoms does not constitute food allergy, highlighting the importance of clinical correlation 1, 5, 11
Cross-reactivity between allergens, such as tree nuts, requires clinical confirmation to ensure appropriate management and avoidance strategies 1
Precautionary labeling, such as "may contain traces," is voluntary and unregulated, creating challenges for allergen avoidance and emphasizing the need for clear labeling and patient education 3, 10