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Food intolerance

Food intolerance is when you have difficulty digesting some foods. You can have an unpleasant physical reaction to them.

It causes symptoms such as bloating and tummy pain. These usually happen a few hours after eating the food.

It's hard to know how many people have a food intolerance. Many people think they have a food intolerance but the cause of their symptoms is something else.

Symptoms of food intolerance

Most people who have a food intolerance have:

The symptoms usually happen a few hours after eating the food.

It can be difficult to know if you have a food intolerance. These symptoms can happen with many other conditions.

Testing for food intolerance

Some companies make food intolerance tests. But these tests are not based on scientific evidence.

These tests cannot diagnose food intolerance. Only your GP or dietitian can diagnose food intolerance.

Find out more about food intolerance testing -

Your GP or dietitian can help you monitor your symptoms and the foods you eat. They may recommend that you stop eating a suspected food for a while. If your symptoms come back when you start eating it again, they can diagnose food intolerance.

Food diary

Try keeping a food diary.

Make a note of:

  • what foods you eat
  • any symptoms you have after eating these foods
  • when these symptoms happen

Trial elimination diet

When you have an idea of the foods that may cause your symptoms, you can try an elimination diet. This means you stop eating the foods 1 at a time and note the effect this has.

Stop eating the suspected food for 2 to 6 weeks and see if your symptoms improve.

Start eating the food again to see if symptoms return. You may find you can tolerate a certain amount and you only get symptoms if you have more than this amount.

A dietitian can help you make sure you get all your recommended daily nutrients while you do this.


Do not restrict your child's diet unless your GP or dietitian recommends it.

Other causes of symptoms

If you often have diarrhoea, bloating, tummy pain or skin rashes but you do not know the cause, see your GP.

Your GP can diagnose the cause from your symptoms and medical history. They may order tests, such as blood tests.

You can also do some research yourself. It may help to find out about other conditions that cause similar symptoms.

For example, find out about:

  • irritable bowel syndrome
  • stress and anxiety disorder
  • lactose intolerance
  • coeliac disease
  • inflammatory bowel disease
  • food allergy

The bowel is a sensitive organ. It's common to have bowel symptoms when you have been ill or feel run down or stressed.

Food intolerance or food allergy

Food intolerance is not the same as food allergy. Here's how to tell the difference.

A food allergy:

  • is a reaction by your immune system (your body's defence against infection) where it treats proteins found in food as a threat
  • can trigger allergy symptoms quickly after eating a very small amount of the food, such as a rash, wheezing and itching
  • is often linked to particular foods - such as fish, shellfish or nut allergies in adults, and milk, egg, fish, peanut or other nut allergies in children
  • can be life-threatening

A food intolerance:

  • does not involve your immune system - there's no allergic reaction and it's never life-threatening
  • causes symptoms that happen over time, often a few hours after eating the problem food
  • only results in symptoms if you eat a large amount of the food - with an allergy, very small amounts can trigger a reaction
  • can be caused by many different foods

Causes of food intolerance

It is often unclear why a person is sensitive to certain foods.

If your symptoms happen after eating dairy products, you may have lactose intolerance. This means your body cannot digest lactose, a natural sugar found in milk, yogurt and soft cheeses. Your GP can usually diagnose lactose intolerance by looking at your symptoms and medical history.

Some people have trouble digesting wheat. They have bloating, wind, diarrhoea, being sick and stomach pain after eating bread.

Other causes can be a food additive, chemical or contaminant, such as:

  • monosodium glutamate (MSG)
  • caffeine
  • alcohol
  • artificial sweeteners
  • histamine, found in Quorn, mushrooms, pickled and cured foods, and alcoholic drinks
  • toxins, viruses, bacteria or parasites that have contaminated food
  • artificial food colours, preservatives or flavour enhancers

Gluten intolerance

Many people cut out gluten from their diet. They think that they are intolerant to it because they have symptoms after eating wheat.

But it's hard to know if the cause of the symptoms is an intolerance to gluten. It could be an intolerance to something else in wheat, or nothing to do with wheat at all.

Very few people need to cut out gluten from their diet. But it's important to do this if you have coeliac disease. Coeliac disease is an autoimmune condition. It's not an intolerance or an allergy.

Living with food intolerance

If you're sure you are intolerant to a particular food, the only way to manage it is by an elimination diet. Check how much of the food you can eat without causing symptoms.

Check food labels to see which sorts of foods to avoid.

If you think your child may have a food intolerance, talk to your GP or dietitian before removing foods from their diet. A restricted diet could affect their growth and development. Cows' milk, for example, is an important source of calcium, vitamin D and protein.

Seeing a specialist

Your GP may refer you to a specialist if they're not sure what's causing your symptoms. You may need more tests.

Your child may need to see a specialist if they have digestive symptoms, such as tummy pain and diarrhoea, and they:

  • are not growing well
  • have not responded to any elimination diets that your GP or dietitian recommended
  • reacted suddenly or severely to a food
  • have a suspected food allergy

Content supplied by the NHS and adapted for Ireland by the HSE

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This project has received funding from the Government of Ireland’s Sláintecare Integration Fund 2019 under Grant Agreement Number 123.

Page last reviewed: 28 February 2022
Next review due: 28 February 2025