Food allergies and intolerances are distinct conditions that are frequently confused. Understanding the difference is clinically important.

Food allergy:

• Immune system response to a food protein
• Can be life-threatening (anaphylaxis)
• Even trace amounts can trigger reaction
• Diagnosed by allergist via skin prick test or blood test (IgE)
• Big 9 allergens: milk, eggs, fish, shellfish, tree nuts, peanuts, wheat, soybeans, sesame

Food intolerance:

• Non-immune reaction — typically enzymatic or chemical
• Not life-threatening
• Usually dose-dependent (small amounts may be tolerated)
• Examples: Lactose intolerance (missing lactase enzyme), gluten sensitivity (non-celiac)

Celiac disease: Autoimmune reaction to gluten. Damages small intestine villi. Affects ~1% of population. Requires strict lifelong gluten avoidance.

Reference:

Wikipedia: Food allergy

https://en.wikipedia.org/wiki/Food_allergy