Food Intolerance


A food intolerance is when you have difficulty digesting certain foods or ingredients in food. It's not usually serious, but eating the food you're intolerant to can make you feel unwell.

Check if you have a food intolerance

If you have a food intolerance, you usually get symptoms a few hours after eating the food or ingredient you're intolerant to.

Common symptoms include:

  • diarrhoea
  • bloating
  • farting
  • tummy pain

But there are lots of other possible symptoms, including headache, feeling tired or exhausted, feeling sick, constipation, joint pain or rashes.

Symptoms can last for a few hours or days.

Food allergy

A food intolerance is different to a food allergy, which causes symptoms such as itchy skin, wheezing or swelling of the lips, face and eyes.

See a GP if:

  • you or your child have any symptoms of a food intolerance that keep coming back

Call 999 if:

  • your lips, mouth, throat or tongue suddenly become swollen
  • you're breathing very fast or struggling to breathe (you may become very wheezy or feel like you're choking or gasping for air)
  • your throat feels tight or you're struggling to swallow
  • your skin, tongue or lips turn blue, grey or pale (if you have black or brown skin, this may be easier to see on the palms of your hands or soles of your feet)
  • you suddenly become very confused, drowsy or dizzy
  • someone faints and cannot be woken up
  • a child is limp, floppy or not responding like they normally do (their head may fall to the side, backwards or forwards, or they may find it difficult to lift their head or focus on your face)

You or the person who's unwell may also have a rash that's swollen, raised or itchy.

These can be signs of a serious allergic reaction and may need immediate treatment in hospital.

Causes of a food intolerance

A food intolerance is caused by your body not being able to digest a certain food or an ingredient in food.

The most common food intolerance is lactose intolerance. This is when your body is not able to digest lactose, a type of sugar mainly found in milk and dairy products such as cheese and yoghurts.

But you can be intolerant to any type of food or ingredient in food, such as:

  • gluten (wheat, rye and barley) – found in foods like bread and pasta
  • histamine – found in foods and drinks like wine and cheese
  • caffeine – found in coffee, tea and some fizzy drinks
  • alcohol
  • sulphites – found in cider, beer and wine
  • salicylates – found in some fruits, vegetables, herbs and spices
  • monosodium glutamate (MSG) – found in ripened fruits, cured meats and savoury foods

Unlike a food allergy, a food intolerance is not caused by your immune system overreacting to certain types of food, which means you cannot have a serious allergic reaction.

Tests for food intolerance

You may be referred to a food and nutrition specialist (dietitian) if a GP thinks you have a food intolerance.

Tests you may have include:

  • a special diet where you avoid eating the food you might be intolerant to, to see if your symptoms get better – after a few weeks you start eating the food again to see if your symptoms return
  • blood tests
  • a breath test if you might be lactose intolerant

You may also be asked to keep a food and symptoms diary to help work out what may be triggering your symptoms.

Home tests

Some tests you can buy that claim to diagnose food intolerances are not recommended.

There's limited evidence that they give accurate results and they may suggest you should avoid multiple foods, which can be harmful.

Treatment for a food intolerance

If you have a food intolerance, try to avoid or reduce eating the food you're intolerant to, including foods where you're intolerant to any of the ingredients.

But it's important to not cut foods out of your or your child's diet without the advice of a GP or food and nutrition specialist (dietitian).

This is because you or your child could miss out on certain vitamins and minerals, which are especially important for a child's growth and development.

The information on this page has been adapted by NHS Wales from original content supplied by NHS UK NHS website
Last Updated: 09/05/2024 10:50:10