Unpleasant reactions to food have long been recognised. The term 'allergy' has been commonly used to describe any adverse or unpleasant reaction to food. However, technically, true food allergy involves the body's immune system and is relatively uncommon. More frequently, some other pathway is responsible for the reaction. It is important to distinguish between different pathways as this can influence the method of diagnosis and subsequent treatment. The term food sensitivity is used to describe any adverse reactions to food irrespective of how it occurs.

The diagnosis of food sensitivity, particularly unsubstantiated self-diagnosis, without medical evaluation and follow-up can led to unnecessarily restrictive and potentially harmful diets. Diagnosis requires careful interpretation of the nature, frequency, severity and duration of symptoms, dietary history, and the results of diets excluding particular foods and the response to their reintroduction. Diets eliminating offending foods should be carefully planned to ensure that all required nutrients can be obtained in adequate quantities, and they should be maintained only under the supervision of a dietitian or doctor. The systematic reintroduction of foods can in some instances provoke serious reactions and should be done under medical supervision.

Sensitivity to food has been associated with a range of conditions including skin (rashes, swelling, hives, eczema), respiratory (asthma, hayfever, sinus trouble), and digestive disorders (diarrhoea, abdominal pain, vomiting) and may be involved in reactions such as headaches, irritability, sleep disturbance, and abnormal behaviour. It must be stressed that there are other causes of these disorders which must be considered before effective treatment can begin. A particular food may provoke no symptoms or varied symptoms from person to person. As children get older, the severity of their allergic reactions sometimes decrease and they can become more tolerant to particular foods.