What’s the difference between a food allergy and a food intolerance?

Niamh Hennessy
Lead Dietitian, Cromwell Hospital
28 March 2024
Next review due March 2027

Symptoms of food allergies and intolerances can be similar. So, it’s not always easy to know which one you might have. But it’s important to get a clear diagnosis. This is because the treatments for each differ. Here, I’ll explain the key differences between food allergy and intolerance, so you know what to look out for.

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What is a food allergy?

With food allergies, your immune system wrongly believes certain food proteins are harmful. When this happens, your immune system overreacts and launches an inflammatory response. This results in the common symptoms of food allergy:

  • itching in the mouth
  • facial swelling
  • difficulty swallowing
  • feeling or being sick
  • tummy pain
  • difficulty breathing
  • dizziness

There are nine main food allergens including milk, eggs, fish, shellfish, tree nuts (such as walnuts) peanuts, wheat, and soybeans.

People with food allergies need to avoid their food allergens completely. This is because sometimes a more severe allergic reaction can occur. This is known as anaphylaxis, a life-threatening condition. Anaphylaxis always requires immediate medical attention.

What is a food intolerance?

If you have a food intolerance, your digestive system finds it hard to digest certain foods. This could happen for a few different reasons:

  • If you have a lactose intolerance, you lack the enzyme lactase. Lactase is needed to break down the lactose (type of sugar) in dairy products.
  • Of you are intolerant to fructose (fruit sugar) your gut may be extra sensitive to certain foods.

Many people can consume small amounts of foods they are intolerant to. Or you might be able to tolerate them in different formats. For example, some people with lactose intolerance can tolerate yoghurt, but not plain cow’s milk.

What are the differences between food allergies and intolerances?

It can be confusing to figure out what’s causing your symptoms after eating. Below you can find a summary of the main differences between food allergies and intolerances.

Food allergy symptoms are usually sudden

With food allergies, symptoms often start soon after eating. This can mean anything from seconds to minutes. Occasionally food allergies show up hours later, but this is less common. With food intolerance, symptoms usually occur several hours after eating. This can help you to tell the difference between an allergy.

Food intolerance symptoms are usually mild

Food intolerance symptoms are usually mild, and can include:

  • bloating
  • gas
  • abdominal pain
  • diarrhoea
  • nausea

Food intolerance symptoms are usually not severe. But, with food allergies, symptoms can range from mild to severe, and may include difficulty breathing or swallowing.

How are food allergies and intolerances diagnosed?

For food allergies known as Immunoglobulin E (IgE) allergies (the most common type), there is a skin prick test or allergy blood test available. These tests will show if you have IgE antibodies. Having these antibodies suggests you are sensitive to specific food allergens. If this matches with your symptoms, you are more likely to be diagnosed with a food allergy.

For food intolerances there is only a reliable test for lactose. Other intolerances are usually suggested after other possible causes have been removed. Sometimes an elimination diet is also recommended. This is where you remove certain foods and record your symptoms at the same time. It is done to help establish a link between what you eat and how you feel.

What’s the treatment for food allergies and intolerances?

If you have a food allergy you must be extremely careful to avoid your allergen(s). This includes avoiding any cross contamination. Small amounts of your allergens could trigger an allergic reaction – sometimes severe. You might also need to take antihistamines or carry an epi-pen (shot of adrenaline) for use in anaphylactic reactions.

With food intolerances there is no medicines or cure. Instead, it helps to reduce your intake of foods that you are intolerant to.

If you have lactose intolerance there are now many different lactose free options available. For example, if you have difficulty digesting fructose, then consuming smaller amounts less often, may help. A dietitian can also help you to create a strategy for managing irritable bowel syndrome (IBS) type symptoms. This often includes adjusting your fibre intake.

If you are having symptoms after eating, then it’s important to see a doctor. They can investigate whether a food allergy or intolerance may be causing your issues, and help you to create a treatment plan, if needed.

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Niamh Hennessy
Niamh Hennessy
Lead Dietitian, Cromwell Hospital



Julia Ebbens, Health Content Editor at Bupa UK

    • Food allergy and intolerance. British association of dietitians., last reviewed March 2024
    • What is a food allergy? Food Allergy Research and Education., accessed March 2024
    • Top 14 food allergens. Allergy UK., accessed March 2024
    • Anaphylaxis. Allergy UK., accessed March 2024
    • Food fact sheet – irritable bowel syndrome and diet. British association of dietitians, accessed March 2024
    • Food allergy testing and diagnosing. Allergy UK., accessed March 2024

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