Many people confuse food intolerances with food allergy but they are not the same and have different causes. This article is intended to help the reader understand those differences. Always consult your doctor if you are worried about symptoms caused by food.
If you have a food allergy, your immune system overreacts to a food by producing antibodies called Immunoglobulin E (IgE). These antibodies activate cells that then release chemicals causing an allergic reaction. This can occur rapidly after exposure to minute amounts of the food. Food allergies may very rarely occur by different immune mechanisms which do not involve IgE. Such non-IgE mediated food allergies tend to be of slower onset, with symptoms taking up to two days to occur, and are often confused with food intolerances.
Food intolerances do not involve the immune system. The symptoms usually occur much more slowly, after eating significant amounts of a particular food, and often because the body is unable to process the food effectively. Many food intolerances involve the digestive system. For example, lactose intolerance is a common condition where a sugar called lactose is poorly digested and thus fermented by gut bacteria. Wheat intolerance is also common, and salicylates within foods can often also cause symptoms. Some think that histamine in food may cause symptoms on rare occasions.
The symptoms caused by food intolerance are varied. Digestive symptoms may include bloating, diarrhoea, nausea or vomiting. Other signs may include fatigue, sluggishness or joint pains.
Symptoms of food allergy usually involve tingling or itching in the lips, tongue, mouth or throat. Abdominal pain, nausea and vomiting can also occur, and sometimes nettle rash (otherwise known as hives or urticaria). More marked symptoms include swelling of the throat causing difficulty breathing, wheezing, chest tightness or breathlessness. These are referred to as anaphylaxis. See the links at the foot of the page for more details about anaphylaxis.
Diagnosing food intolerance
There is no validated test for food intolerance, and the clinical diagnosis can only be made after excluding known causes. It is important to get expert medical advice, and the doctor’s approach in the case of a child may need to be different to that taken with an adult patient. Tests used to diagnose food allergy – skin prick tests and blood tests – are not able to diagnose a food intolerance. Over-the-counter testing or methods suggested on the Internet should be viewed with great suspicion and not used as there is no evidence that they are of any value. However a well-trained healthcare professional may be able to tell from what the patient reports whether the reaction is driven by the immune system or not; and if a food intolerance is suspected, an elimination and reintroduction diet may be suggested. This is where the suspect food is cut out of the diet and later reintroduced to see if symptoms occur.
If you believe you may suffer from a food intolerance, it is important not to restrict your diet without getting expert advice.
Another common cause of symptoms triggered by a food is a psychological aversion to that food, usually the result of an adverse experience earlier in life. For example, if you become sick after eating a food you might have an aversion to that food in the future – even if the illness was not caused by the food. Symptoms of food aversion occur only when the food is knowingly eaten. This is not allergy.
Read our factsheet about anaphylaxis here.
This article has been reviewed by Dr Paul Williams, Consultant Clinical Immunologist, Department of Immunology’ University Hospital of Wales. Other members of the Anaphylaxis Campaign’s expert clinical panel offered views on an earlier draft.
All the information we produce is evidence based or follows expert opinion and is checked by our clinical and research reviewers. If you wish to know the sources we used in producing any of our information products, please let us know, and we will gladly supply details.
The information provided in this Factsheet is given in good faith. Every effort has been taken to ensure accuracy. All patients are different, and specific cases need specific advice. There is no substitute for good medical advice provided by a medical professional.
About the Anaphylaxis Campaign: Supporting people with severe allergies
The Anaphylaxis Campaign is the only UK wide charity to exclusively meet the needs of the growing numbers of people at risk from severe allergic reactions (anaphylaxis) by providing information and support relating to foods and other triggers such as latex, drugs and insect stings. Our focus is on medical facts, food labelling, risk reduction and allergen management. The Campaign offers tailored services for individual, clinical professional and corporate members.
Published: May 2019
Review date: May 2022