What is the difference between an allergy and intolerance?


A true food allergy causes an immune system reaction that affects numerous organs in the body. It can cause a range of symptoms including difficulty breathing, exhaustion, headaches, migraines, itchy skin, hives, furry tongue, blurred vision, pain and digestive issues. In some cases, an allergic reaction to a food can be severe or even life-threatening.


In contrast, a food intolerance is generally less serious and often limited to digestive issues (symptoms such as bloating, flatulence, abnormal bowels, cramping, reflux etc). In the case of a food intolerance, individuals may be able to eat small amounts of the offending food without trouble. In addition, the intolerance may be prevented through taking supplements, for example digestive enzymes, where there is sugar malabsorption.


Food allergy = immune system reaction to a food

Food intolerance = inability to digest a food

Diagnosis of a food allergy or food intolerance:

Food allergies are diagnosed by either a Skin Prick Test or a blood test, carried out by an Allergist or Immunologist. These tests measure the level of immunoglobins (called IgE, IgG and IgA) antibodies which your immune system produces in response to a food trigger. IgE usually mediates an immediate response and is often called a "true allergy". IgG and IgA blood testing is available but it is not diagnostic of food hypersensitivity or allergy. While blood testing is available for food intolerance reactions (some kits test over 90 different foods), these tests are controversial as the results are commonly not reproducible and are not as reliable as food challenges, failsafe diets or elimination diets for uncovering food sensitivity. So diagnosis of food intolerances is best carried out by an Accredited Dietitian or Nutritionist skilled in the area of conducting food challenges.

Most common food allergies or intolerances include:


  • Cow’s milk/products

  • Eggs

  • Peanuts / tree nuts (such as cashews or walnuts)

  • Fish

  • Shellfish

  • Gluten (see coeliac disease page)

  • Wheat

  • Soy

  • Yeast


Other intolerances we often see in our practice:



The sugar found in milk products. When there is a shortage of the enzyme lactase in the brush border of the small intestine an individual will not be able to digest and absorb lactose properly. Symptoms include bloating, flatulence, upset stomach, and diarrhea. These symptoms can be resolved by avoiding dairy foods, taking a digestive enzyme which contains the lactase enzyme at the same time as consuming diary foods, or choosing “lactose free” milk and yoghurt.


Cow’s milk protein

Casein A1 protein found in cow’s milk (except Jersey and Guernsey cows that produce A2) is indigestible in the human gut. Some individuals, most commonly children under the age of two years, react negatively to the ingestion of this protein. Symptoms may include upset stomach, skin disorders, gut discomfort or abnormal stools. For such individuals, avoidance is necessary. If found to be a problem in young children, a food challenge later in life is worthwhile to assess whether tolerance has increased.


Food additives

Additives in processed foods most commonly linked to an intolerance include artificial colours (tartrazine 102, Quinoline yellow 104, Carmoisine 122, Brilliant Blue 133, Brown HT 155) flavours (Glutamates including MSG 620-625, Ribonucleotides 627, 631, 635) and artificial sweeteners (Acesulphame-K 950, Aspartame 951).



Preservatives commonly found in wine and dried fruit, and also naturally occurring in other foods. Their numbers are 220-228 and appear in the ingredient list. Sulphite reactions cause asthma, rashes, irritable bowel syndrome and headaches in sensitive people. Sulphur in medications and household products can induce severe, and sometimes immediate reactions. A Dermatologist can help diagnose allergic reactions to chemicals and household products, particularly if you get a skin reaction (e.g. hives, eczema, rash).


What to eat?


This is where a Dietitian can help. If you suspect a mild food allergy, or intolerance, a Dietitian will request you keep a food and symptom diary to record all of the foods you eat and drink to pinpoint the culprit(s). Your Dietitian will also obtain an intensive personal and family history to help draw conclusions around what you may be reacting too. Food challenges designed for the individual will confirm any intolerances or sensitivities. Alternatively, an elimination diet may be followed, with subsequent food challenges to find out if symptoms return.

Many children "grow out" of their food allergy as their immune and gut system develops, so for many kids it is not necessary to avoid a allergen food for life. Some people with adult onset food allergies or intolerances may find the opposite happens, and that as they get older they need to be extra careful and seek extra dietary advice. In either case, regular visits to your dietitian and Immunologist can ensure that you are not unnecessarily avoiding foods, and that you continue to avoid or limit the ones that matter.

Reference/further reading

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