Food intolerances

Food intolerance is an adverse reaction to a food. Unlike food allergies, intolerances do not involve the immune system. Find out about types of food intolerance and the symptoms.

Symptoms of food intolerance

Reactions to food intolerance can be delayed for several days and the reaction is usually dependent on the amount of food eaten. Symptoms of food intolerance include:

  • skin – rashes
  • respiratory – asthma, sinusitis, nasal congestion
  • gastrointestinal – nausea, vomiting, diarrhoea, constipation, gas, abdominal pain
  • other – headaches.

Types of food intolerance

Food intolerance can be divided into several groups:

  • enzyme deficiencies
  • allergy-like intolerances
  • food chemical intolerances
  • sulphites.

Enzyme deficiency

If an enzyme in your digestive system is missing or not functioning correctly, it won't be able to help digest the food it is associated with. This will cause digestive-related symptoms such as diarrhoea, bloating, wind and abdominal pain.

The most common enzyme deficiency is lactase, which causes lactose intolerance. Lactase digests the milk sugar lactose. Usually people can still tolerate small amounts of lactose-containing foods.

Other enzyme deficiencies are rare, but fructose, maltose and sucrose intolerances do sometimes occur. See your doctor or dietitian if you suspect lactose intolerance.

Allergy-like intolerances

Some reactions to foods that commonly cause allergy, such as milk, wheat, egg and soy, are actually intolerances. These will not appear on allergy tests but can be tested for using atopy patch tests. This involves applying a paste of the suspected food to a patch of skin on your back and then monitoring for reactions over hours. These tests are only done by a specialist. Intolerances to foods are most easily diagnosed by an elimination diet under the supervision of a dietitian.

Food chemical intolerance

The 2 main classes of chemicals that occur naturally in foods are salicylates and amines. These can affect or cause asthma, pruritus, hives, eczema and migraines.


Sulphites in food are required to be listed on food labels, although sulphite reactions are not due to an allergy, but intolerance.

Sulphites are preservatives used most commonly in wine, dried fruit and sausages. The additive numbers are 220 to 228. Sulphites will appear as one of these numbers in ingredient lists on food labels. Above a certain level, labels will say 'contains added sulphites'.

Sulphites mainly cause asthma in sensitive people, but may also cause rashes, irritable bowel syndrome and headaches.

Who to contact

If you have questions about food intolerances, email

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