Food Allergy vs. Food Intolerance... What Is The Difference?

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One in five Australians has some kind of allergy. For food allergies specifically, the prevalence is lower with one in 20 children and one in 100 adults reporting an allergic reaction to food. The prevalence of food intolerance however is believed to be much higher. But what is the difference? And does it even matter?

Yes, it does matter. Adverse food reactions is the name given to food allergies and food intolerances.(1) Acknowledging the difference between an allergy and an intolerance is important as they often require different management strategies.

dairy cow

An example
Allergy to cow’s milk (an allergy) is very different to an intolerance of the lactose in cow’s milk (intolerance). For those with a severe allergy to cow’s milk, avoiding cow’s milk (and goat and sheep milk too) completely is an appropriate treatment. However, a person with lactose intolerance will generally manage to eat low-lactose foods that are made from cow’s milk (e.g. hard cheese, lactose free milk) without problem.


Allergies are becoming more and more common these days(2) and the prevalence of allergy in Australia and New Zealand are amongst the highest in the developed world.(3)

An allergy refers to the body’s immune system having an abnormal reaction to substances that are usually harmless.(2) The substance to which an allergic person reacts is known as an allergen. The allergen can be a variety of things such as dust mites, pets, foods, medicines, moulds, insects, etc.(2) Allergic reactions vary in their severity from being very mild to life-threatening. The major food allergens are peanut, tree nuts, sesame seed, milk, fish, shellfish, wheat, and soy.

Broadly speaking, allergies can be classified into two groups: IgE-mediated reactions and non-IgE mediated reactions, based on what is happening in the body.(4) IgE refers to the class of immunoglobulin (antibody). There are five classes of immunoglobulins (A, D, E, G and M) and when the immune system is functioning normally, their role in the body is to protect against bacteria and viruses.

An IgE-mediated reaction is sometimes called a ‘true allergic reaction’.(1)  When someone who has an Ig-E mediated allergy comes into contact with the allergen, cells in the immune system react abnormally and release chemicals, the main one being histamine. These chemicals are what cause the symptoms of an allergic reaction. Symptoms usually present immediately or up to two hours after contact with the allergen and can include:(1)


Non-IgE mediated reactions are generally not life threatening but can be harder to diagnose than the IgE-mediated reaction. This is because symptoms usually take longer to arise (many hours) and skin-prick tests (the usual way of diagnosing an IgE-mediated reaction) are most often negative, making it harder to pin-point the cause.(4)

A common example of a non-IgE reaction is an infant’s reaction to cow’s milk or soy. Symptoms include bloody diarrhoea, vomiting, irritability, failure to thrive or abdominal distention.(5)  Diagnosis is made when symptoms resolve with the removal of milk and soy from the infant’s diet (and/or that of the mother if she is breastfeeding). This is followed later on by a dietary challenge to confirm the diagnosis.(4)

Another example of this type of reaction is Coeliac Disease. Coeliac disease is an adverse reaction to gluten, a protein found in wheat, rye, barley and oats that results in damage to and inflammation of the lining of the small intestine. Coealiac Disease is NOT a wheat allergy. Symptoms may include malabsorption, diarrhoea, abdominal distention, weight loss or failure to thrive.(5) Whilst a blood test can tell you that you may have Coeliac Disease, for the diagnosis to be confirmed a Gastroenterologist must perform an endoscopy and take multiple biopsies of the small bowel.

Food intolerances

Food intolerances describe a non-immune adverse reaction to food.(1) Some common symptoms include hives, headaches, sinus problems, mouth ulcers, abdominal pains, bowel problems and generally feeling unwell.(6) Some people experience only mild symptoms whereas others experience more severe symptoms. Similarly, the amount of the problem food that causes a reaction is different for each person – some people can tolerate a little of the food, some more and some none at all.

Food intolerances can arise due to a range of factors such as:
•    Enzyme deficiency: Enzymes break down food so it can be absorbed by the small bowel. A low level or lack of a certain enzyme means that the particular food component cannot be absorbed and this can cause symptoms such as bloating, wind, diarrhoea and abdominal pain.(1) For example, lactose intolerance is due to low levels of lactase, the enzyme whose job it is to break down lactose.
•    Reactions to food additives such as colours, preservatives and flavour enhancers: These may cause a range of symptoms. A common concern relates to sulphites which are used as a preservative in a wide range of foods. Sulfites are most often associated with a worsening of asthma symptoms in sensitive asthmatics but have not been found to cause asthma.(7)
•    Food chemical intolerance: Foods naturally contain chemicals such as salicylates, amines and glutamates. It has been reported that certain people react to one or more of these food chemicals(8) although this is not universally accepted in the scientific literature.(9)
•    FODMAPs™ intolerance: This is an acronym given to a group of carbohydrates that occur in a wide range of foods that have recently been found to be associated with Irritable Bowel Syndrome (IBS) in some people.

Skin prick test

Diagnosing and managing food allergies

Several clinical tests are used to diagnose food allergies, in conjunction with your medical history. Skin Prick Tests are a common test(10) that involve a concentrated allergen extract being placed on the skin and a small prick being made through the drop. If you are allergic, a lump (wheal) will appear. Another common test is a blood test, also known as a RAST test. The RAST test measures IgE antibodies for specific allergens.

There are many unproven allergy tests available. These include cytotoxic food testing, kinesiology, Vega testing, pulse testing, reflexology and hair analysis.(10) IgG/IgG4 antibody blood tests are often touted now as being able to diagnose food allergies, however in reality all this tells you is whether or not you have been exposed to the allergen, but does not tell you whether you have an allergy or intolerance to that food.(11) There is no good evidence suggesting that IgG tests can diagnose allergic disease.(11)

Allergies are managed by avoiding the food altogether. Fortunately in Australia, all packaged food that is labelled must identify the top allergens in bold type in the ingredients list and with a warning statement. Adhering to a diet that requires strict avoidance of an allergen can be hard, especially in social situations, and it has been associated with psychological distress.

skin test

Diagnosing and managing food intolerances

Food intolerances cannot be tested for using the same tests as food allergies. Food intolerances are diagnosed using an elimination diet whereby the suspect food/group of foods is eliminated from the diet.(4, 6) If symptoms resolve during the elimination phase, a challenge is then conducted to determine which food/group of foods is the culprit and to establish individual tolerance levels. Sometimes complete avoidance of the problem food/food groups is not necessary. It is essential that any elimination diet is undertaken under the guidance of a dietitian to ensure that nutritional balance is maintained – especially for children who need all the nutrients to support their growth and wellbeing.

Choosing the right tests and the right management strategy is important. Eliminating foods unnecessarily can result in diets that are nutritionally unbalanced, can make enjoying social aspects of food challenging and may even lead to psychological distress. For children in particular, getting the diagnosis and the treatment right is important for supporting optimal growth and nutrition.


Words by Anna Millichamp

Anna Millichamp


Anna Millichamp is an Accredited Practising Dietitian (APD) and Accredited Nutritionist (AN). Her business, Create Nutrition, is located in Byron Bay. Combining her experience in both Paediatric and Adult nutrition with her love of tasty, healthy food, Anna helps her clients achieve better health one bite at a time.

Create Nutrition, PO Box 5, BYRON BAY NSW 2481
M: 0466 090 289 E: This email address is being protected from spambots. You need JavaScript enabled to view it. blog

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1.    Mahan KL, Escott-Stump S. (2008) Krause's Food & Nutrition Therapy. 12th ed. Missouri: Saunders Elsevier.
2.    Australasian Society of Clinical Immunology and Allergy (ASCIA). (2010) What is Allergy? Factsheet.
3.    Access Economics Pty. Ltd. for Australalsian Society of Clinical Immunology and Allergy (ASCIA). (2007) The economic impact of allergic disease in Australia: not to be sneezed at: ASCIA.
4.    Jyonouchi H. (2008) Non-IgE mediated food allergy. Inflammation & Allergy - Drug Targets;7:1-8.
5.    Motala C. (2004) Food Allergy. World Allergy Organization; Available from:
6.    Royal Prince Alfred Allergy Unit. (2006) Food Allergies & Intolerances: From 'Friendly Food'.  Sydney: Sydney South West Area Health Service; Available from:
7.    Australasian Society of Clinical Immunology and Allergy (ASCIA). (2010) Common Myths about Allergy and Asthma Exposed. Available from:
8.    Swain A. (1988) The role of natural salicylates in food intolerance. Available from:
9.    Jansen SC, van Dusseldorp M, Bottema KC, et al. (2003) Intolerance to dietary biogenic amines: a review. Annals of allergy, asthma & immunology : official publication of the American College of Allergy, Asthma, & Immunology;91(3):233-41.
10.    Australasian Society of Clinical Immunology and Allergy (ASCIA). (2010) Allergy Testing. Available from:
11.    Australasian Society of Clinical Immunology and Allergy (ASCIA). (2007) Unorthodox Techniques for the Diagnosis and Treatment of Allergy, Asthma and Immune Disorders Available from:


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