Introduction to adverse reactions to food

Many people associate various symptoms to foods, and while scientific evidence that foods can be harmful is lacking in many cases, there is evidence to support some adverse reactions to foods, including:

Adverse reactions to foods can be categorised into several groups.

Food allergies

These reactions are caused by immune reactions to foods which a patient is allergic to. Symptoms can include skin reactions such as urticaria and eczema, rhinitis and asthma, as well as the most serious reaction, or anaphylaxis. Foods implicated include nuts (such as peanuts and tree nuts), shellfish, fruits (such as strawberries), eggs, milk and others.

Specific food intolerances

Adverse reactions to foodsSome people are not able to tolerate certain foods because they are unable to process them normally in the body. People with coeliac disease cannot tolerate gluten (found in wheat and other foods) as it damages the small intestine and prevents absorption of other nutrients and causes several symptoms such as poor weight gain in children, abdominal distention and diarrhoea. People with lactose intolerance cannot have milk and milk products in large amounts as they lack the enzyme required to digest lactose. See the articles on coeliac disease and lactose intolerance for more information.

Sensitivities to food additives

Some people suffer from reactions to certain food additives, which are added to food to improve flavour, colour, texture, as preservatives or to improve nutritional value of foods. Reactions may be due to an allergy to a particular substance, resulting in symptoms similar to those seen in patients with food allergy, or may be due to other mechanisms resulting in a variety of symptoms.

Sensitivities to natural food chemicals

Many natural chemicals found in foods also have the ability to cause adverse reactions, in particular salicylates and amines. Food intolerances can cause headaches, bowel irritation or upset, mouth ulcers, hives and sensations of being generally unwell. The natural chemicals in foods can be as much of a problem for people who are sensitive to them as artificial food additives. See the article on adverse reactions to natural food chemicals for more information.

Other reactions not clearly defined

Some people claim that symptoms or conditions such as irritable bowel syndrome are made worse by eating certain types of food, however these foods tend to be different for different people, and there are no consistent findings that certain foods should be avoided in these people. Similarly, some people with migraine find that certain foods act as a trigger, such as chocolate, cheese and wine, however the mechanisms for this are not clear (though they may be related to natural food chemicals, see above).

More information

For more information on nutrition, including information on types and composition of food, nutrition and people, conditions related to nutrition, and diets and recipes, as well as some useful videos and tools, see Nutrition.


  1. Kumar, P. Clarke, M. Clinical Medicine. 5th ed. 2002. WB Saunders.
  2. Loblay, Swane, Souter. 2 Food. 2004. Murdoch Books.
  3. Simon, R. Adverse reactions to food additives. 2005. UpToDate.

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