Food Allergy or Food Intolerance?

Dr. John Hsiang

Dr. John Hsiang

Livingstone Digestive & Liver Clinic

Dr. John Hsiang is a gastroenterologist and hepatologist with more than 15 years of clinical experience. His clinical interests include managing fatty liver disease, viral hepatitis, Helicobacter pylori infection, and effects of the gut microbiome on irritable bowel syndrome and has extensive experience in gastrointestinal cancer screening.

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It’s a special occasion and you’ve decided to celebrate at an Italian restaurant. A hearty dinner of pasta and pizza later, you return home only to be troubled by a lingering sensation of fullness in your belly that only seems to grow in discomfort as time passes. Alarmed by stories you’ve read online about the scary things that can happen to people with food allergies, you rush to your nearest gastroenterologist prepared for the worst.

You might be surprised then to find out, that what you have is merely an intolerance (to gluten specifically), and not an allergy. But what are the differences between these commonly misunderstood conditions?

Intolerance vs Allergy

1. The Science

An allergic reaction occurs when the body’s immune system responds needlessly to substances that would normally be considered harmless – a case of mistaken identity essentially.

Let’s say someone with a mild peanut allergy accidentally pops a Reese’s Peanut Butter Cup. Within a few seconds to more than an hour after ingestion, the immune system begins to overreact. Antibodies known as Immunoglobulin E are produced, which then bind to specific chemical compounds in the peanut product, triggering the release of histamines in bulk.

These histamines act in a myriad of ways to give rise to the telltale signs of allergic reaction. They stimulate nerve endings in the skin, resulting in that unpleasant itching or burning sensation. They cause the leakage of fluid from blood vessels into surrounding tissue, bringing about a runny nose, watery eyes and swelling in the form of hives.

In extreme cases, the flood of histamines can precipitate anaphylaxis, a severe type of allergic reaction characterised by swollen tongue and lips, shortness of breath, plummeting blood pressure and a rapid but weak pulse. This is considered a medical emergency.

Conversely, food intolerances are conditions of the digestive system. They are the result of either the body’s inability to properly digest certain chemical compounds present in food, or the irritation of the digestive tract by said compounds.

Take lactose intolerance for example. Lactose is a ubiquitous sugar naturally found in milk and other dairy products. Lactose intolerant individuals do not produce lactase, a digestive enzyme that typically helps to break down lactose in the small intestine. Hence, when your lactose intolerant brother washes down his lunch with a milkshake, the undigested lactose passes into the large intestine, where it is fed upon by bacteria, bringing about symptoms of gassiness, bloating and diarrhoea.

2. Frequency

Fortunately, food allergies are much rarer than food intolerances. Food allergies are estimated to affect only 2.5% of the global population according to the World Allergy Organisation. On the other hand, approximately 20% of the global population has suffered from a food intolerance at one point or another in their lives.

3. Dosage

“There’s only a little bit inside, don’t worry.” If only this were the case. To those with food allergies, even a trace amount of allergen is enough to trigger an adverse reaction. Therein lies the danger of cross contamination. If, for example, the hawker at your favourite economy rice stall uses the same pair of tongs to handle the various dishes prepared, it is entirely possible for your seafood allergy to flare up even if you do not order any seafood at all.

Food intolerances however are often dose related; individuals with a food intolerance may not exhibit any symptoms at all unless a large quantity of the offending food item is consumed, or if it is consumed very frequently.

Living With My Condition

The best way to prevent an allergic reaction is to simply avoid the corresponding allergen. This is, however, easier said than done. While individuals with food allergies can do their due diligence by inspecting the labels of food products before purchasing them, things become complicated when food preparation is left in the hands of others.

Not only is it difficult to guarantee zero cross-contamination, the cooks themselves may not be fully aware of the exact ingredients of a particular dish, especially if components of the dish are prepared off-site and delivered over. Add on the language barrier when communicating with foreign service staff, and the need to repeatedly check and double check with each new eatery, and allergic reaction increasingly becomes a matter of when, not if.

This is why those who suffer from severe food allergies – and are willing to shoulder the monetary cost – choose to carry around an EpiPen at all times. A portable auto-injector designed for rapid delivery of the drug epinephrine (you might know it as adrenaline), the EpiPen is used in the event of extreme allergic reaction to effectively alleviate the life-threatening symptoms of airway swelling and low blood pressure.

Management of food intolerance follows a similar path – simply avoid consuming the food that you are intolerant to (though the consequences of failing to do so are far more forgiving, so you won’t have to walk on eggshells every time you eat out).

Lactose and gluten-free substitutes of common foodstuffs like milk and cereal are also commonly sold in grocery stores, ensuring that the lifestyle changes that come naturally with a food intolerance diagnosis are more manageable.

Early Detection

Unfortunately, definitive silver bullets for food allergy and intolerance have yet to be developed. Nevertheless, with early detection, it may be possible to manage your condition with greater foresight. Should you experience hives, stomachache, prolonged bloatedness or vomiting after a meal, it would be wise to pay a visit to your nearest allergy clinic or gastroenterologist for a professional opinion. Here, it is important to take note that while allergists specialise in allergy management, gastroenterologists are more experienced in the food intolerance management.

Food intolerance is often determined through extensive history taking and a process of trial and error – you may be asked to keep a food diary of what you eat and when you experience your symptoms, or to go on an elimination diet, where you completely exclude the suspect food entirely until you are symptom-free, before slowly re-introducing said food to more accurately pinpoint the culprit.

With regards to food allergies however, testing is available to narrow down the exact allergen involved, for example, the skin prick test, where a needle is used to prick a small amount of the suspected allergen beneath the skin, before observing the injection site for any welts or bumps. Blood tests to screen for allergen-specific antibodies are also common.

Add on a healthy dose of preventative education, and you’re ready to start your journey towards well-rounded food allergy or intolerance management on the right foot.

Article reviewed by Dr John Hsiang, Senior Consultant Gastroenterologist at Livingstone Digestive & Liver Clinic.


  1. U.S. Department of Health and Human Services. (2017, July 21). Understanding Food Allergies. National Institutes of Health. Retrieved April 20, 2022, from
  2. Mayo Foundation for Medical Education and Research. (2020, August 4). Allergies. Mayo Clinic. Retrieved April 20, 2022, from
  3. Gardner, A. (n.d.). Anaphylaxis (anaphylactic reaction): Symptoms, causes, treatment. WebMD. Retrieved April 20, 2022, from
  4. Immunoglobulin E (IGE) defined. American Academy of Allergy Asthma & Immunology. (n.d.). Retrieved April 20, 2022, from,-Asthma-Immunology-Glossary/Immunoglobulin-E-(IgE)-Defined#:~:text=If%20you%20have%20an%20allergy,throat%2C%20or%20on%20the%20skin.
  5. Administrator. (2021, March 30). Hives (urticaria). Australasian Society of Clinical Immunology and Allergy (ASCIA). Retrieved April 20, 2022, from
  6. Fowler, P. (n.d.). Histamines: What they do, and how they can overreact. WebMD. Retrieved April 20, 2022, from
  7. Holland, K. (2018, September 17). Timeline of an anaphylactic reaction. Healthline. Retrieved April 20, 2022, from
  8. WebMD. (n.d.). Food allergy and food intolerance – causes, symptoms, treatments. WebMD. Retrieved April 20, 2022, from
  9. MediLexicon International. (n.d.). Food intolerance: Causes, types, symptoms, and diagnosis. Medical News Today. Retrieved May 25, 2022, from
  10. Food intolerance: Symptoms, causes and treatment options. Cleveland Clinic. (n.d.). Retrieved May 25, 2022, from
  11. Kubala, J. (2018, January 25). The 8 most common food intolerances. Healthline. Retrieved May 25, 2022, from,their%20wide%20range%20of%20symptoms.
  12. Food allergy. WAO. (n.d.). Retrieved May 25, 2022, from,from%201%25%20to%2010%25.
  13. What is an epipen and who needs it? Atlanta Allergy & Asthma. (n.d.). Retrieved April 20, 2022, from
  14. U.S. National Library of Medicine. (2021, September 7). Food allergy testing: Medlineplus Medical Test. MedlinePlus. Retrieved April 20, 2022, from
  15. James Myhre & Dennis Sifris, M. D. (n.d.). What causes a food allergy? Verywell Health. Retrieved April 20, 2022, from,than%20men%20or%20vice%20versa