Food allergies affect around 5% of adults and 8% of children, with growing evidence of an increase in prevalence, according to a study by the National Center for Biotechnology Information in America. But what causes an allergic reaction to food? And what can be done to diagnose and treat food allergies?

An allergic reaction to a specific food is caused by an abnormal response from your immune system when you ingest the problematic-food. Your immune system will wrongly recognise some of the proteins in a specific food as harmful to your body. It will then activate a range of defence mechanisms, such as the release of chemicals like histamine, which causes inflammation.

Which foods are the culprits?

While any food has the potential to trigger an allergic reaction, the most common food allergies are limited to eight foods: Wheat, milk, eggs, peanuts, tree nuts, shellfish, soy and fish. Eggs, wheat, dairy and soya are often outgrown in childhood, whereas nut and fish allergies often persist into adulthood.

Because food allergies are immune-mediated, even a tiny amount of allergen may trigger a reaction.

What are the symptoms to look out for?

An allergic reaction to food can either affect the skin, the gastrointestinal tract, the neurological or cardiovascular systems, or the respiratory tract. Symptoms can occur anywhere from a few minutes to a few hours after exposure to the food.

These symptoms may include:

  • Skin: Eczema, hives and swelling of the face;
  • Gastrointestinal: Nausea, vomiting or diarrhoea;
  • Neurological: Dizziness, anxiety or loss of consciousness in the event of anaphylaxis;
  • Respiratory: Coughing, wheezing and sneezing;
  • Cardiovascular: Wheezing, shortness of breath or fall in blood pressure;
  • Anaphylaxis: Life-threatening, extreme reactions involving any of the above, requiring emergency treatment. Read more about anaphylaxis here.
It’s important to distinguish between food intolerance and a food allergy

Food intolerance may involve some of the same signs and symptoms as food allergies, so the two can often be confused. For example, in lactose intolerance, sufficient quantities of the lactose enzyme reduce the ability to digest lactose, the main sugar in milk products. This can result in bloating, cramping and diarrhoea.

If you have a food intolerance, you may be able to eat small amounts of the offending food without any trouble. You may also be able to prevent a reaction. For example, if you have lactose intolerance, you can use lactose-free dairy products or take lactose enzyme pills (Lactaid) to aid digestion, reports Mayo Clinic.

It’s also important to consider the possibility of food poisoning being confused for an allergic reaction. For example, if you do not adequately refrigerate certain fish, like tuna or mackerel which contain high amounts of bacteria, high levels of histamine that trigger symptoms like the ones we see with food allergies. We refer to this as histamine toxicity or scombroid poisoning.

Certain food additives, such as sulfites used to preserve dried fruit, canned goods and wine can trigger asthma attacks in sensitive people. Additives such as monosodium glutamate (MSG), artificial sweeteners and food colourants can also cause severe reactions.

If you have trouble figuring out if you are intolerant or allergic to a specific food, a proper diagnosis from an allergy doctor will give you clarity.

Who is at risk for food allergies?

If you have a family history of allergic diseases such as asthma, eczema, hives or a previous food allergy, it’s important to be aware of the possibility of an allergy. Allergic reactions like asthma or eczema may be more severe with food allergies, and children, especially toddlers and infants, are at a higher risk than adults.

Those more at risk of developing anaphylaxis are asthmatics, teenagers or young children.

Diagnosing and treating food allergies

An essential part of food allergy diagnosis starts with obtaining a thorough history. Be prepared to answer questions about your family’s allergy history; when your symptoms began; the severity of your symptoms; how long it took to trigger the symptoms; what medications you have taken; and how your body reacted to these medications.

The following measures might also be taken to make a diagnosis:

  • A physical examination to identify or exclude other medical problems, such as asthma or allergic rhinitis;
  • Compiling a food diary, which can help establish your eating habits, symptoms and medications to pinpoint the problem;
  • A skin prick test, to provide clarity about your reaction to a particular food. It’s important to note a positive response to this test alone isn’t enough to confirm a food allergy;
  • An elimination diet to link symptoms to specific foods. A particular food may be recommended to be avoided entirely for two weeks to see if the allergic reaction will stop;
  • Blood tests to look at the number of allergy-type antibodies (IgE) in the blood;
  • An oral food challenge may also be recommended. During this test, done in a doctor’s office, small increasing amounts of the suspect food is given over several hours to confirm if a food allergy exists.
In conclusion

Food allergies can’t be cured, and it’s essential to have a proper medical diagnosis to confirm your food allergy because you might not be allergic at all. A correct diagnosis by an allergy doctor or another medical doctor can be the first step towards treating and controlling your body’s reaction to a specific food. You’ll also have the peace of mind of knowing which foods to avoid, and what to do when your allergic reaction occurs.

© 2018 | Dr Marinda McDonald | Practice number 0015393 | All rights reserved

  • The purpose of this article is to raise awareness of allergies and the treatment options that are available for it. This article should by no means be used, or viewed, as a primary source for medical advice – please arrange for a personal consultation with your medical practitioner before taking any decisions that could affect the wellbeing of you or your loved ones. Read our medical disclaimer for more information.

Marinda McDonald

Dr Marinda McDonald has offered specialised treatments for allergies for most of her professional career. Read more about her on the home page of this website (


Lebogang Mahlangu · May 10, 2019 at 8:36 pm

Always knows what your allergies are to avoid being at risk

    Hlengiwe Thembi Nani · May 29, 2019 at 9:01 pm

    I think I must really be aware what my 12year son eats..the problem is at school.I am not always there around to guide him…he had excyma before..his throat is always blocked..especially at night.

How six, non-allergenic cupcakes burst my medical bubble (and renewed my respect for allergy moms) | The Allergy Clinic · July 17, 2019 at 9:06 am

[…] usually reassure my patients with food allergies that searching for the right ingredients shouldn’t take longer than an additional 45 minutes. […]

Podcast: The ins and outs of allergies | The Allergy Clinic · July 31, 2019 at 8:45 am

[…] And then Dr. McDonald and Kathy also talk about a variety of allergies – from dust mite to bee allergies, food allergies and skin conditions associated with […]

Answering common questions about food allergies | The Allergy Clinic · August 30, 2019 at 9:19 am

[…] do food allergies come […]

Oral immunotherapy: The pros, cons and risks | The Allergy Clinic · February 10, 2020 at 9:30 am

[…] is a viable option to treat peanut, egg and milk allergies. According to medical studies, between 60% to 80% of patients have been treated […]

Comments are closed.