Understanding food allergies and intolerances

Food allergies and intolerances may seem similar, but they have different causes and involve different responses in the body. A food allergy is caused by the immune system, and can result in a severe response to the allergenic food. A food intolerance results in a much less severe response, as it does not involve the immune system. 
Food allergies

During an allergic reaction to food, antibodies (proteins that can bind to foreign substances in the body) bind to proteins in the food that cause an allergy (allergens). These antibodies then bind to certain immune cells. This activates the immune cell to release histamine, which causes the symptoms of food allergy. The only solution to prevent symptoms is to avoid the foods that you are allergic to. Common symptoms of a food allergy include:

    • Dizziness

    • Prickling sensation in the mouth 

    • Problems swallowing

    • Red and itchy skin

    • Swollen face, mouth or elsewhere

    • Vomiting

    • Anaphylaxis


The immune system response to the food allergen is usually quick, but can also start up to two hours after eating. The most severe response is anaphylaxis, in which someone experiences a decrease in blood pressure and constricted air flow caused by histamine. Someone in anaphylactic shock needs treatment with epinephrine immediately to open up the airways and increase the heart rate. 

Food allergies can be diagnosed by either a skin-prick test or a blood test. For a skin-prick test, the allergen is pricked into the skin. If someone is allergic, a reaction will appear on the skin. In the blood test, the amount of antibody against food allergens is measured in the blood. If someone is allergic to a certain food, the amount of antibodies against that food is higher. In a food challenge, the food will be given by a medical professional, to determine if any symptoms appear. 

The likelihood of outgrowing a food allergy varies between foods. Children are most likely to grow out of egg, milk and wheat allergies, but are less likely to outgrow peanut and soy allergies, and very few outgrow fish, tree nut, molluscs or shellfish allergies.

Common food allergens include:

    • Celery 

    • Eggs

    • Fish

    • Gluten containing wheat

    • Lupine

    • Milk

    • Molluscs 

    • Mustard

    • Peanuts

    • Sesame

    • Shellfish

    • Soy

    • Sulphite

    • Tree nuts

These foods are legally required to be mentioned on the labels of food products, so allergens can be avoided. 


Food intolerances

Unlike food allergies, food intolerances are not caused by an immune system reaction. If you have a food intolerance, your body cannot properly digest a food, or part of a food. This is mainly caused by non-functional enzymes, but can also be caused by active ingredients in food – such as histamine. 

Common symptoms of a food intolerance include:

    • Bloating 

    • Diarrhoea

    • Stomach ache

    • Rashes

    • Headache

Although food intolerances do not cause severe symptoms like anaphylaxis, they can certainly result in discomfort, therefore foods causing intolerances should be avoided. As food intolerances do not involve the immune system, the response is not as rapid. Symptoms can appear immediately after eating, but can also take up to 24 hours to present. 

Food intolerances are usually diagnosed by excluding the food from the diet for a few weeks, and determining if your symptoms improve. This can be done by an exclusion diet, such as the FODMAP diet, where many foods are excluded from the diet, and later gradually re-introduced. By tracking the symptoms, the foods causing an intolerance can be identified. Lactose intolerance can be diagnosed by a breath test, which measures hydrogen produced by bacteria in the gastrointestinal system. Unlike food allergies, food intolerances are usually lifelong and cannot be outgrown. 

Foods and food components that commonly cause a food intolerance include: 

    • Alcohol

    • Certain fruits

    • Eggs

    • Food or flavour additives

    • Lactose

    • Salicylate

    • Sulphite

    • Wine (histamine)



Overall, food allergies are caused by the immune system, with reactions occurring quickly after eating, can be outgrown and can result in severe responses. Food intolerances are mostly caused by non-functional enzymes, cannot be outgrown, symptoms often take longer to develop and result in discomfort. Both allergy and intolerance symptoms are usually best avoided by avoiding the foods causing them.




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