Food Intolerance vs Food Allergy vs. Food Sensitivity

Published date: March 22, 2013 | Modified date: October 29, 2019

What is a food allergy?

This is one of my favorite topics. It’s incredibly important for millions of people, most of whom don’t even know it yet, and it’s a very confusing topic.  To set the stage, lets’ first talk about food allergies.

A food allergy is when a person has trouble breathing because of swelling of the tongue or throat (this is an anaphylactic reaction) after eating a food, or they get asthma, a rash, hives, a runny nose, or eczema as a result of eating a particular food.

Food allergies are defined by having an IgE antibody and histamine reaction to a food, and that reaction resulting in one of the symptoms above.  This is an inflammatory response to the food, produced by the immune system.

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The words ‘food allergy’ have become defined more by tradition than by science. Only these specific symptoms, and only positive IgE lab results or positive skin prick/patch testing will result in the diagnosis of a food allergy, as noted in the Journal of Allergy and Clinical Immunology. So when a medical professional uses the words ‘food allergy’ they are usually referring only to a reaction resulting in one of those symptoms – anaphylaxis, asthma, eczema, rash, runny nose, or hives.

This sounds fine. However, IgE reactions can also result in other types of symptoms, such as migraines, as described in the medical journal Annals of Allergy, and esophageal reflux, described in the medical journal Pediatrics International, as well as many other symptoms. Reactions such as these are much less likely to be diagnosed by an allergist, because it is not part of their paradigm, and therefore less likely to be termed a ‘food allergy.’

For example, if you had headaches and you happened to have a positive IgE test result showing an allergy to dairy, it’s unlikely that the allergist would even consider that your headaches could be caused by a dairy allergy.  It’s simply not part of their world. Strange, but true. And most other doctors also would not connect the lab results to your symptoms. It’s not part of their training.

Complicating this is that even though IgE reactions are inflammatory reactions, they are not the only type of inflammatory reactions that can be triggered by food. Many other types of inflammatory reactions against food also exist, some of which are described by Dr. Sabra in Annals of Allergy and by Dr. Nowack in the Journal of Allergy and Clinical Immunology. These include IgA and IgG antibody reactions, as well as many other types of immune reactions. When these reactions are diagnosed, if they are diagnosed at all, they may or may not be termed ‘food allergies.’

Of course, the public cannot be expected to keep up with all of this, nor should you. And to add to all of the confusion the words ‘food allergy’ are often used by the general public to describe other reactions to foods, regardless of the type of symptom they are experiencing or the type of testing that was performed, if any was performed at all.

In our experience, there are at least a hundred different symptoms that can result from a food reaction, and it is not at all unusual for people to experience these reactions.  You can read more about these on our web page, Common Symptoms of Food Allergies.

When food is broken down and absorbed, it is distributed via your bloodstream throughout your body. Since your immune system is everywhere in your body, the inflammatory response to that food can be anywhere. Therefore, a reaction can occur anywhere in your body. We don’t understand why a food allergy can exhibit itself so differently in different people, but it is clear that it can. Every individual is unique and seems to have a unique weak point where symptoms of a food allergy show up.

What is a Food Intolerance?

A food intolerance is a reaction to food that is not considered an allergy but is well accepted by the medical community, such as a gluten intolerance or lactose intolerance.

Food intolerances are not defined by any common underlying medical cause or mechanism of action. They simply are not food allergies. Therefore, it is important to understand food allergies in order to understand a food intolerance. (See ‘What is a Food Allergy?’ above.)

Let’s look at some examples of food intolerance. There are two very good examples, one of which everyone has probably heard about, lactose intolerance, and the other most are familiar with, gluten intolerance. Let’s first consider lactose intolerance.

Lactose intolerance is well understood to be a deficiency in the enzyme needed to digest lactose. Lactose is a sugar in milk. If you don’t produce enough of the enzyme, called lactase, then you can’t digest lactose and you end up with gas, bloating, and abdominal discomfort when you ingest milk products, as described by the American College of Physicians. It’s about as simple as that.

To solve this problem, you can buy lactose-free milk and you will be fine. You can also buy the enzyme and take it with your food, and it will help you digest milk products and you’ll be fine.

Note however that lactose intolerance has nothing to do with the immune system. It doesn’t produce inflammation. It doesn’t cause any real damage.  It’s definitely not life-threatening. It’s just very uncomfortable and perhaps embarrassing. It’s not an allergy and should not be confused with a dairy allergy, which is an inflammatory reaction to dairy. (Note: A dairy allergy can cause the same symptoms as a lactose intolerance, and can also cause many other symptoms.)

Now let’s turn to the second example, gluten intolerance. Gluten intolerance is not an enzyme deficiency. Gluten intolerance is an immune reaction to protein in wheat and related grains. And in the case of celiac disease, it results in an autoimmune reaction.

Antibody production is also involved, but these are not the IgE antibodies we noted when discussing the traditional definition of food allergy. These are IgA or IgG antibodies, also produced by the immune system. Gluten intolerance also involves other parts of the immune system beyond the production of these antibodies.

Gluten intolerance is not just a digestive problem. Many people who are gluten intolerant don’t have any digestive problems at all. And people who are gluten intolerant may experience any one of hundreds of different symptoms.

Gluten intolerant people can experience digestive problems, skin problems, neurological problems, psychological problems, weight problems, etc. The list goes on and on. A gluten intolerance can cause headaches, diarrhea, joint pain, fatigue, depression, and a hundred other symptoms, as described by Dr. Green in the New England Journal of Medicine.

As you can now see the use of the word ‘intolerance’ in lactose intolerance is something completely different than the use of the word ‘intolerance’ in gluten intolerance.

I find this frustrating. It’s very inconsistent and very confusing. And you have probably already guessed it, but there is no scientific definition for the word intolerance, or at least not one that is being followed. It means the same thing in this context as it does anywhere else in the English language. It’s just a very broad word that means that someone isn’t happy.

What is a Food Sensitivity?

The words ‘food sensitivity’ are usually used as an umbrella term to describe any type of food reaction, especially one not defined as a food allergy or recognized by the medical community as a food intolerance. However, many people include allergies and intolerances when speaking of food sensitivities.

‘Sensitivity’ is often used by the average Jane to indicate that she knows that she just doesn’t do well with a particular food, but she doesn’t quite know what to call it. She’s not comfortable calling it an allergy or an intolerance.

There is no clear medical definition of food sensitivities. There has been a small movement in the medical community to use the word sensitivity when describing certain gluten reactions, as seen in the title of the research article Nonceliac Gluten Sensitivity, in the medical journal Gastroenterology.

This does little to help us understand these terms and is likely the result of the words ‘gluten intolerance’ already being the accepted term for celiac disease. Therefore, the author felt that nonceliac gluten reactions (reactions to gluten in people who don’t have celiac disease) had to be called something other than intolerance and settled on ‘sensitivity.’

Making sense of it all

At this point, you either understand or are completely confused. I’m hoping that you have a much better comprehension of the history behind the use of the words allergy, intolerance, and sensitivity. That’s helpful. If we’re going to educate the world about our reactions to food then we need a consistent, scientific, and meaningful language with which to converse about it. We need a foundation on which we can build. Otherwise, these topics are going to continue to dwell in the cellar of our medical system.

Surprise! Someone has taken care of this problem. No, it wasn’t me. Although I’d love to take credit for it, I’m just the town crier. Two panels of experts, one in Europe and one in the U.S., in 2001 each came out with very comprehensive and well thought out position papers on exactly this subject. A huge thank you to  Drs. Sampson, Sicherer, and Birnbaum of the American Gastroenterology Association and to the European Journal of Allergy and Clinical Immunology.

Their conclusions were nearly identical. First, they started with the word sensitivity. Sensitivity is an umbrella term. It encompasses all food reactions. That makes sense. Food sensitivities are then broken down into two major categories – immune reactions and non-immune reactions.

All immune reactions are essentially considered a type of allergy, regardless of which part of the immune system is involved. These immune reactions are then further subdivided by the mechanism underlying the immune reaction (allergy). This is where it gets a little technical because some knowledge of the immune system is required. However, it helps us to categorize different types of allergies. For example, we have IgE reactions, IgA reactions, IgG reactions, etc. It is important to note that celiac disease has clearly been categorized as an allergy, which is logical because it is an immune reaction.


This breakdown of food reactions was published nearly 20 years ago. Unfortunately, it seems that not much has been done with the standards that were developed. The time has come for us to do just that. Without a clear language, we will continue to talk circles around the issue of food sensitivities, the public will continue to be confused, and doctors will continue to add to the confusion.

Please spread the word. A lot more than semantics is at stake. I estimate that the health of half the population is tied to these issues. Together we can help educate the public and the medical profession and make the world a much safer place in which to eat.


There is very little consistency or standardization in the use of the words ‘allergy,’ ‘intolerance,’ and ‘sensitivity.’ The general public may use any of these words interchangeably, and who’s to blame them? With such a lack of standardization and poor reasoning for using any of these terms, it’s difficult to understand them even if that is the goal.

We need much clearer usage of these terms from the medical community. They are unnecessarily complicated and almost impossible to follow due to inconsistent use both clinically and in the medical literature. This is not only making it difficult to discuss reactions to foods but is impacting our ability to grow in our understanding and knowledge of reactions to foods, which should be of utmost priority in health care.

In the meantime, please have patience with your doctors. They probably don’t even realize why there is so much confusion.