There is a possibility that either you are or you may know anyone who experiences discomfort after consuming a particular food. These unpleasant symptoms can be vomiting, rashes, itching, bloating, sneezing, swelling in the tongue or any other symptom. 

These may occur when the person is either allergic to or intolerant to that food. Food allergy and intolerance terms are often used interchangeably but there is a huge difference between the two.

Non-toxic adverse reactions caused as a consequence of immunological mechanisms, after the intake of specific foods is referred to as food allergy. But food intolerance is associated with our digestive system in which digestion related issues occur. 

Food Allergy 

Food allergy is also known as hypersensitivity. Food allergy is the abnormal response of our immune system to a particular food. As soon as our immune system detects the presence of an antigen or foreign bodies like bacteria, viruses, etc., it stimulates the production of antibodies to fight these. Antibodies are immunoglobulins and Immunoglobulin E (IgE) is primarily responsible for allergic reactions in our body. Therefore, allergy or allergic reaction occurs when IgE fights against this food, sensing it incorrectly as some harmful substance for our body. It is scientifically referred to as an IgE-mediated reaction. Food or substance to which a person is allergic is called an allergen. Apart from IgE-mediated reactions, these allergens also stimulate our immune cells in response to which inflammation-causing mediators also produced. Some of the common symptoms of food allergy are -

1. Gastro-intestinal Symptoms - Abdominal pain, diarrhoea, vomiting, nausea and gastrointestinal bleeding.

2. Skin Symptoms - Itching, rashes, eczema, inflammation, redness and swelling of blood vessels.

3. Respiratory Symptoms - Wheezing, breathlessness, coughing and running nose. 

4. Systemic Symptoms - Hypotension and death.

5. Neurological Behaviour - Headache, restlessness and irritability.

Therefore, it is very important to address the food allergy as soon as the symptoms appear as it might prove fatal at times if left untreated.

Food Intolerance 

Food Intolerance is a response of our digestive system to a particular food. It is a non-allergic response in which our body is unable to digest or metabolise any food component resulting in a physical reaction. For example, lactose intolerance is when the person is unable to digest lactose sugar present in milk due to the deficiency of any enzyme - lactase, required to digest lactose. Food intolerance can occur due to various factors.

1. Enzyme deficiency - The food we eat is broken down and absorbed under the presence of many digestive enzymes that assists in the better utilisation of nutrients in the body. Hence, due to lack of an enzyme, our body is unable to digest it and reaction can occur in the form of cramps, vomiting, diarrhoea and abdominal pain. For example, phenylketonuria is an example of an inborn error of metabolism in which the body is unable to metabolise phenylalanine amino acid due to enzyme deficiency. Since our body is unable to break it down, hence accumulation occurs resulting in brain damage and eczema.

2. Naturally occurring food chemicals - Many substances are produced in the foods during processes like fermentation, ageing, storage, etc. These may result in food intolerance at times. For example, histamine can occur in high levels in some cheese and wines. People intolerant to histamine in high quantities may experience discomfort on consuming such foods.

3. Food additives - Packaged and processed foods have become an inevitable part of our daily diet. Food companies add various food additives like artificial sweeteners, preservatives, stabilisers, artificial food colours, flavours, taste enhancers and thickeners. These at times may cause reactions among people who are intolerant to any component of an additive. 

4. Microbial contamination - Intake of contaminated food due to improper handling or storage can also lead to intolerance as microbes present in the food may cause breakdown leading to food degradation. For example, scombroid fish poisoning.

5. Unable to digest food - At times, our body is unable to digest foods when consumed in large quantities. This can lead to bloating and flatulence. For example, bacterial fermentation within our body on consuming foods rich in fructose, cellulose, sorbitol and xylitol.

To sum up, food allergy and intolerance are completely different from each other. Generally, food intolerances are observed when large quantities are consumed. But during food allergy, even a tiny strain of that food component can trigger our immune system. Therefore, in case of any symptom, it is very important to consult a doctor so as to determine whether the patient is food allergic or intolerant.  


Food Allergy. (2018, October 29). NIH: National Institute of Allergy and 

Infectious Diseases.

Tuck, C. J., Biesiekierski, J. R., Schmid-Grendelmeier, P., & Pohl, D. (2019). Food Intolerances. Nutrients, 11(7), 1684.

Food Intolerance. Australasian Society of Clinical Immunology and Allergy (ASCIA). (2019).

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