Food allergy is an immune system response — specifically IgE-mediated. The immune system mistakenly identifies a food protein as a threat and produces antibodies (IgE) against it. On re-exposure, even tiny amounts trigger histamine release: symptoms appear within minutes to two hours and can range from hives and swelling to anaphylaxis (a severe, life-threatening reaction). Common allergens include peanuts, tree nuts, milk, eggs, wheat, soy, fish, and shellfish.
Food intolerance does not involve the immune system. It is dose-dependent (small amounts may be tolerated), delayed (symptoms often take hours), and not life-threatening. Examples: lactose intolerance (insufficient lactase enzyme to digest milk sugar), fructose malabsorption, sensitivity to histamines in fermented foods, and the diverse triggers captured by the FODMAP framework.
The distinction matters clinically. A person with a peanut allergy must carry an adrenaline auto-injector and strictly avoid all exposure. A person with lactose intolerance can usually eat hard cheese and yoghurt without symptoms.
“Intolerance” and “allergy” are often used interchangeably in everyday speech, causing real confusion. If you suspect a significant food allergy, seek formal allergy testing (skin-prick or specific IgE blood tests) through a clinician rather than self-testing. Unnecessary food elimination based on unvalidated tests can lead to nutritional inadequacies.