Differences between Food Allergy and Food Intolerance

Comparison Article

A food allergy is an adverse health effect arising from a specific immune response that occurs reproducibly on exposure to a given food. This reaction happens when the body's immune system mistakenly identifies a protein in a food as a threat, triggering the release of chemicals like histamine. In contrast, a food intolerance is a physiological reaction that does not involve the immune system. It typically occurs when the digestive system cannot properly break down a certain food, often due to enzyme deficiencies or sensitivity to specific substances.

While some symptoms can overlap, the underlying mechanisms and potential severity of the two conditions are different. Allergic reactions can affect multiple body systems and may lead to anaphylaxis, a severe and potentially life-threatening condition. Food intolerances primarily affect the digestive system, and while they can cause significant discomfort, they are not life-threatening.

Comparison Table

Feature	Food Allergy	Food Intolerance
Body System Involved	Immune system	Digestive system
Underlying Cause	Immune system mistakenly identifies a food protein as harmful, releasing IgE antibodies and histamine.	Difficulty digesting a food, often due to enzyme deficiencies (e.g., lactose intolerance) or sensitivity to additives or natural chemicals.
Onset of Symptoms	Usually rapid, within minutes to two hours after consumption.	Generally slower, occurring several hours or even days after consumption.
Amount of Food to Trigger Reaction	A microscopic amount can cause a reaction.	A person may be able to eat small amounts without a reaction; symptoms are often dose-dependent.
Common Symptoms	Hives, itching, swelling of lips or face, trouble breathing, wheezing, vomiting, dizziness.	Bloating, gas, diarrhea, constipation, stomach pain, headaches.
Severity	Can range from mild to severe and life-threatening (anaphylaxis).	Not life-threatening, though symptoms can cause significant discomfort.
Diagnosis	Skin-prick tests and blood tests that measure specific IgE antibodies.	Often diagnosed through an elimination diet, after ruling out other conditions. There are no reliable diagnostic tests for most intolerances.

Venn diagram comparing Differences between Food Allergy and Food Intolerance

Mechanism

A food allergy is an IgE-mediated immune response. The immune system produces Immunoglobulin E (IgE) antibodies that react to a specific food. These antibodies attach to immune cells, and upon subsequent exposure to the allergen, they trigger the release of chemicals that cause allergic symptoms.

A food intolerance stems from the digestive system's inability to process a food. This can happen for several reasons. For example, lactose intolerance is caused by a deficiency of the enzyme lactase, which is needed to break down the sugar (lactose) in milk. Other intolerances can be caused by reactions to natural chemicals in foods, like histamine, or to additives such as sulfites.

Diagnosis

Diagnosing a food allergy typically involves a review of the patient's history along with specific tests. Skin-prick tests or blood tests can measure the presence of IgE antibodies to particular foods, helping to confirm an allergy.

Diagnosing a food intolerance is often more complex. Because it does not involve a measurable immune response, allergy tests are not effective. The most common method for diagnosis is an elimination diet, supervised by a healthcare professional, where suspected foods are removed from the diet and then gradually reintroduced to observe for symptoms.