Food allergy or intolerance?

A woman holding stomach due to food allergy

Do you feel uncomfortable or unwell after eating certain foods? Maybe you’re wondering if you’ve got a food allergy. Or a food intolerance.

Many people believe they’ve got one or other of these conditions. Yet they may not be sure what the difference is.

And it is confusing, especially as some symptoms are common to both conditions. But what’s going on inside your body is very different. Food intolerance affects 15-20% of the population. It means you have trouble digesting certain foods.

This might produce annoying and unpleasant symptoms. Food allergy stems from an overactive immune system and can be life-threatening. Around 4-6% of children and 4% of adults in the US have diagnosed food allergies.

It’s important to find out the root cause of your symptoms so you can get the best advice about treatment options.

Food intolerance definition

Food intolerance is the same as food sensitivity. It means you struggle to digest a particular substance such as lactose, gluten or histamine. That may be because of an enzyme deficiency. For instance, you need the enzyme lactase to process the milk sugar lactose. People who don’t make enough lactase may feel bloated and get diarrhoea when they eat dairy products.

Food intolerance symptoms can also stem from something called visceral hypersensitivity. This is when your brain is hyper-aware of your digestive system working. So you feel the processes of digestion more which can be painful. Irritable Bowel Syndrome often comes with visceral hypersensitivity. You may get symptoms when you try to digest the fermentable carbohydrates (FODMAPS) found in many common foods.

People with food intolerance may actually be able to tolerate a certain amount of the offending food before they get symptoms. It varies from person to person.

Food intolerance

Common symptoms

Mild to moderate, often starting a few hours after eating

  • Bloating and tummy pain
  • Wind and diarrhoea
  • Skin rashes and itching

No reliable medical test except breath test and blood test for lactose intolerance

An elimination diet helps make a diagnosis


Talk to a dietician or nutritionist before changing your diet. They may suggest eating less of the problem food until your symptoms are manageable. Or eating it in a different form (cheese instead of milk, for instance)

Food allergy

Common symptoms

Moderate-severe and start in minutes – or sooner

  • Tingling or itching in the mouth
  • A raised, itchy red rash (hives) – sometimes the skin can turn red and itchy without a raised rash
  • Swelling of the face, mouth, throat or other parts of the body
  • Difficulty swallowing
  • Wheezing or shortness of breath
  • Feeling dizzy and lightheaded
  • Feeling sick (nausea) or vomiting
  • Abdominal pain or diarrhoea

IgE antibody test: commonly a skin prick test or allergy blood test


The best way not to have an allergic reaction may be by avoiding the food that causes it. But talk to your healthcare provider first. Antihistamines can help ease mild to moderate allergy symptoms. Your healthcare provider may also prescribe an auto-injecting adrenaline pen to carry in case of a severe allergic reaction

Symptoms for food tolerance

Food intolerance symptoms can be hard to distinguish from other conditions. A helpful clue is they tend to start a few hours after eating. Doctors call this slow onset. That’s different from food allergy symptoms which are usually quick onset. You might get any of these effects:

  • Bloating and tummy pain
  • Wind and diarrhoea
  • Skin rashes and itching

Symptoms of food intolerance may be mild to moderate: they’re annoying but not usually severe.

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Food boxes in kitchen in yellow

Is there a test for food tolerance?

Testing for food intolerance is not as advanced as it is for food allergy. In fact, there’s no reliable test yet for any intolerance except lactose. For this, your healthcare provider may suggest a hydrogen breath test. Or they may check your blood sugar levels after asking you to drink a lactose solution or milk.

None of the other tests offered for food intolerance are medically proven. That includes IgG and IgG4 blood tests. These types of tests may show you have an antibody response to certain foods. But studies suggest this might be because you’ve met this food in the past. It’s a sign your body is doing what it should and you’ve built up a tolerance rather than an intolerance.

Hair strand analysis and kinesiology aren’t regarded as reliable tests either. Positive results can lead people to cut whole food groups from their diet without needing to.

So how do I find out if I have a food intolerance?

A commonly used approach is the elimination diet. Putting short-term restrictions on what you eat helps identify food intolerances if you have them. A typical elimination diet might include: 

  • Cutting out foods that cause food intolerance symptoms
  • Slowly reintroducing these foods while monitoring your symptoms
  • Calculating how much of a problem food you can tolerate and in what form
  • Drawing up a long-term management plan for your food intolerance

It’s a good idea to talk to a nutritionist or dietician first. Managing an elimination diet on your own can be tricky. There are hidden sources of food sensitivities in food and drink; for instance flavour enhancers or thickeners. Your GP may be able to refer you to a nutritionist in your area.

Quote Image

People struggling with intolerance often assume they’ll have to give up certain foods. But the idea is to find your tolerance level and keep food on the menu where possible.

Managing food intolerance

People struggling with food intolerance often assume they’ll have to give up certain foods to control their symptoms. But that’s not always the case. The elimination diet helps you find your individual tolerance level. The idea is to keep foods on the menu where possible. You may need to eat smaller portions less often or a different form. For instance, hard cheese tends to be easier to digest than milk and sourdough than ordinary bread.

Unfortunately, there’s no cure for food intolerance at the moment. You will always be susceptible to having symptoms if you go over your personal threshold for the problem food.

With lactose intolerance, your healthcare provider may suggest taking lactase enzymes to help you digest dairy products.

3 common types of food intolerances

  • Lactose: You may lack the enzyme necessary to digest the natural sugar in milk and dairy products like yoghurt and soft cheese. Lactose intolerance is more common than milk allergy which is when your immune system reacts to milk protein.
  • Wheat and gluten: Distinguishing which of these you may be sensitive to can be a challenge but it is helpful. You may only need to cut back on wheat and not all foods containing gluten. To add to the confusion celiac disease also has some symptoms in common with gluten sensitivity. This is not an allergy or an intolerance but an autoimmune condition triggered by eating gluten.
  • Histamine: Diamine oxidase (DAO) helps digest histamine. Not having the enzyme can make you sensitive to wine, chocolate and fermented foods including cheese, chocolate, beer and wine, soy sauce and sauerkraut.
Bearded man scratching his head. He’s clearly baffled about the difference between sensitization and allergy.

Sensitized: what does it mean?

Food additives like monosodium glutamate and colorings can also cause food intolerance symptoms. So can stimulants such as caffeine or alcohol.

Food allergy vs intolerance: what’s the difference?

Food allergies are an immune system reaction. The job of your immune system is to defend your body against viruses, parasites, bacteria and other threats. Sometimes it makes a mistake. You eat a harmless peanut, say, and it goes on full alert, producing antibodies called Immunoglobulin E (IgE). Eat a peanut again and these antibodies release histamine and other chemicals to get rid of it from your body.

A tiny trace of your food allergen can be enough to trigger a reaction. Food allergy symptoms usually start quickly. And they can be severe, even life-threatening. There is another type of allergic reaction that doesn’t involve IgE antibodies where symptoms can take several days to show. But this non-IgE-mediated food allergy is less common.

Food allergy symptoms

People with food allergies tend to know they’ve eaten the wrong thing within minutes or even seconds. This is a much faster response than with food intolerance. Symptoms can include:

  • Tingling or itching in the mouth
  • A raised, itchy red rash (hives) – sometimes the skin can turn red and itchy without a raised rash
  • Swelling of the face, mouth, throat or other parts of the body
  • Difficulty swallowing
  • Wheezing or shortness of breath
  • Feeling dizzy and lightheaded
  • Feeling sick (nausea) or vomiting
  • Abdominal pain or diarrhoea
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Food allergy can also cause a severe allergic reaction called anaphylaxis. This may be life-threatening without medical attention. Call 991 immediately if you or someone you’re with get any of these symptoms:

  • Skin reactions, including hives and itching and flushed or pale skin
  • Drop in blood pressure (hypotension)
  • Constriction of your airways and a swollen tongue or throat, which may cause wheezing and trouble breathing
  • A weak and rapid pulse
  • Nausea, vomiting or diarrhea
  • Dizziness or fainting

Which food causes allergic reactions?

You can be allergic to any food but some allergies are more common. By law, food packaging and restaurant menus must highlight these major allergens if they are an ingredient.

There are eight on the list: fish, shellfish, tree nuts, peanuts, milk, eggs, wheat and soybean. Sesame will join them in 2023.

People with pollen allergy may find that eating some fruit, veg, spices, legumes (peanuts and soybeans) and nuts gives them a tingly mouth. For instance, if you’re allergic to birch pollen and eat an apple. For instance if you’re allergic to ragweed and eat honeydew, cantaloupe or water melon. It happens because the food and your trigger pollen contain similar proteins. These cross-reactions are known as pollen food syndrome or oral allergy syndrome and are usually mild.


Understanding the difference between food sensitivities and allergies is important. An allergy test won’t tell you if you have an intolerance. And the treatment options are different.

Can you test for food allergies?

Yes, unlike food intolerance there are reliable ways to test for allergies. Your healthcare provider may suggest skin prick testing or a blood test. With a skin prick test the doctor puts drops of liquid, each one containing a possible allergy trigger, onto your arm. Then your skin under each drop is gently pricked. A small itchy red bump means you’re likely to have an allergy to that substance. Blood tests look for the IgE antibodies.

A positive result from a skin prick test or a blood test means you’re sensitised to that substance. It doesn’t mean you have an allergy or will definitely develop one. It is up to your doctor to interpret the results for you. They’ll ask about your symptoms and medical history, and whether allergy runs in the family, to help them make a diagnosis.

Taking an allergy test won’t tell you whether you have a food intolerance (sensitivity).

Treatments for food allergy vs intolerance

Understanding the difference between food sensitivities and allergies is important because the treatment options are different. Modifying how much you eat certain foods, in what form and how often may be enough to calm the symptoms of food intolerance. If you have an allergy, it’s best to scan food labels and menus so you can avoid trigger foods completely. In either case, talk to a dietary or medical expert first.

There are also medications that can help ease milder symptoms of food allergy. Histamine is a chemical your body releases as part of an allergic reaction. Antihistamine can block its effect. Many types of antihistamines are available over-the-counter so ask your pharmacist for advice. If your healthcare provider thinks there’s a risk of anaphylaxis, the most severe type of reaction, they’re likely to prescribe an auto-injecting adrenaline pen for you to carry with you at all times. As for long-term treatment, the first food-related allergy immunotherapy won FDA approval recently. Its aim is to desensitise children who have a peanut allergy to an accidental exposure to the substance.

If you suspect a food allergy or intolerance ask your healthcare provider to help you figure out what's actually causing your symptoms. Together you can then find a way to deal with them effectively.

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