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The Difference Between Food Allergy and Food Intolerance

Erica Dermer

Medically reviewed by

Stefano Guandalini, MD


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What happens when a food you love doesn't love you back?

Do you get a stomachache or troubling gastrointestinal issues when you eat something in particular? Or maybe it's a migraine or a skin rash when you eat a take-out? Sometimes it's difficult to understand what's happening when you eat something and your body goes haywire.

Chances are, most of us have an offending food that just doesn't sit right with our body. But do you know if it's a food intolerance or a food allergy? And what's the difference?

It turns out that adverse reactions to food are common - and they run the gamut from mild to deadly. But not all reactions to food are necessarily allergies, and not all reactions to food means that you can never have that food again. Because of this, your reactions to foods should be investigated to see if they are true allergic reactions, or if there is another cause to your digestive discomfort. 

Food allergy vs food intolerance: The short definition

Definition of a food allergy

Broadly speaking, a food allergy is an over-reaction from the body’s immune system in response to a food protein which triggers an allergic reaction. In some cases, a food allergy can cause potentially life-threatening symptoms, in others, symptoms may be less obvious.

Definition of a food intolerance

A food intolerance, on the other hand, is a reaction to a food that does not involve the immune system. Reactions can sometimes be immediate or appear 10-20 hours after eating. Symptoms of a food intolerance can often be vague or even mimic the symptoms of other ailments.

The exact difference between them

The differences between true allergies and intolerances are the different pathways that they work in the body. While you may think of a food ‘allergy’ as a one-size-fits-all word, it really depends on how the body views the offender, and what system the body uses to mount an attack against it. 

In this guide you’ll find the exact definition of an allergy vs an intolerance along with symptoms and specific nuances between the two and how they both cause your body to react.

Ways your body can react to food

There are several ways in which you can have an issue with food - and it’s all about how your body reacts to it. 

Here's a quick example of a bodily reaction:

If your immune system overreacts to a food allergen by producing antibodies called Immunoglobulin E (IgE), then you have an allergy.

These antibodies travel to cells that release chemicals, including histamines, causing an inflammation that is defined as an allergic reaction. Here are common examples of the different ways your body can react negatively to a certain kind of food: 

Immunoglobulin E (IgE) mediated (Allergy)

This is what is considered a true food allergy. The body’s immune system will begin overproducing antibodies to fight against an offender. But the offender is an everyday food, like a peanut or a glass of milk, instead of a virus or bacteria. This type of allergy can risk anaphylaxis (aka the most severe, life-threatening allergic reaction), that can begin within minutes of food consumption.

Non-IgE mediated (Allergy)

In these conditions, the body’s immune system will react, but the IgE antibodies (like the example above) are not involved in this type of allergic reaction - and thus would not show on an IgE test. These types of reactions include oral allergy syndrome and the serious FPIES (Food Protein Induced EnteroColitis Syndrome) diagnosed in infants as a reaction often to milk, soy, or cereal grains. 

Mixed IgE mediated (Allergy)

There are conditions that can occur as either an IgE- or as a non-IgE-mediated reaction. A good example is Eosinophilic Esophagitis (EOE). EOE, also called “the asthma of the esophagus”, can cause food impaction and dysphagia - where it feels like food is stuck in your throat. Those with EOE can be treated by an elimination diet (a diet that excludes the most common offending foods such as wheat, milk, egg, nuts, soy, fish and shellfish) or by some drugs, like steroids. Typically, one or more repeat biopsies every few months are necessary to monitor the disease regression. 

Non-immune mediated (intolerance)

These common reactions are not involving the immune system. These reactions typically happen in the digestive tract - based on the food that you consume. These are the difficult reactions to discover without the help of some physician-guided detective work. These include issues with the digestive processes like lactase deficiency, sucrase-isomaltase deficiency. You can also have a histamine intolerance and thus react to foods rich in histamine (e.g. aged cheeses), or issues with food additives or food coloring. When we talk about food intolerances - we’re typically talking about non-immune mediated food issues. 

An immune reaction represented by autoimmunity (autoimmune)

This is where the body attacks itself after consuming a certain food, as seen in celiac disease as a result of consumption of gluten. While it’s not at all a true ‘allergy’, some celiacs say that they are “allergic to gluten,” because the body reacts to the protein with many gastrointestinal and also general symptoms. However, this is a lifelong autoimmune condition with a genetic basis that cannot be outgrown and as of now, cannot be treated by any other means than permanently eliminating all sources of gluten.

Let’s talk in more detail about the differences between some of these food issues. 

What are food allergies? 

Allergies are a common condition, where an allergen triggers an adverse reaction in the body. According to AAAAI, "an allergic reaction typically triggers symptoms in the nose, lungs, throat, sinuses, ears, lining of the stomach or the skin."

A food allergy can be defined by the rapid activation of antibodies to specific foods that – even in very small amounts - cause the body to react in different ways ranging from mild to very serious reactions. Over 32 million Americans are living with potentially life-threatening food allergies.

Although there are more than 170 foods that have been identified as causing an IgE-mediated reaction, by far the most common are cow’s milk, soy, wheat, eggs, fish, shellfish, peanuts, tree nuts and sesame.

Food allergy symptoms

It’s important to note that there are not mild to severe true food allergies - only mild to severe reactions to foods. These reactions usually have a rapid onset within minutes to hours. The most common manifestations of food allergy involve the GI tract: 

  • Nausea
  • Vomiting
  • Abdominal pain
  • Diarrhea
  • Skin swelling or hives
  • Coughing, wheezing
  • Swelling of the airways

A severe food allergic reaction might also result in anaphylaxis – an acute-onset, life-threatening reaction that involves many organs at the same time. Unfortunately, allergic reactions are hard to predict, and a previously mild reaction can sometimes turn into a dangerous one. This is why food allergies must be taken seriously. 


Why do food allergies develop?

Food allergies can develop soon after birth or arise later in life, as in the case of adult-onset allergies. Scientists do not yet fully understand how someone develops or is at risk for food allergies. Research is currently being done to evaluate risk factors for developing allergies like the hygiene hypothesis, environmental exposure, genetics, maternal diet during pregnancy, timing of food introduction, and breastfeeding status.

The cause of a food allergy comes from an immune system that mistakes a food protein for an infectious threat. Anyone can be affected by a food allergy, whose prevalence is constantly increasing, especially for males and those of Asian and Black ethnicity. As said before, while many foods can cause allergies, these nine types of food are the most common allergenic foods:

  • Dairy
  • Wheat
  • Soy
  • Eggs
  • Fish
  • Shellfish
  • Peanuts
  • Tree nuts
  • Sesame

Unlike a food intolerance, symptoms of a food allergy usually occur even with small amounts of a ‘trigger’ food, and symptoms are brought on very quickly. 


Diagnosing and treating food allergies

There are no standard criteria for the diagnosis of food allergies, and several ways of testing for food allergies. Even according to FARE, one of the top food allergy non-profits organizations, “current methods of diagnostic testing for food allergy are often inconclusive.” 

Diagnosis is further complicated by the fact that even detecting high levels of food specific IgE in your blood does not necessarily indicate clinical allergy but could instead be a sign of sensitization (your body reacting to eating the food often). Because of these issues, diagnosis requires a careful medical history, physical examination, appropriate laboratory tests - like an IgE allergy test, and in many cases, an oral food challenge might be deemed necessary by your physician to confirm a diagnosis. 

“Be mindful of the fact that many tests that claim to diagnose food allergy are actually not valid, including: Hair and urine analysis, electrodermal testing, applied kinesiology (where they test muscles strength and weakness as a way to diagnose allergy) Or, measuring food-specific IgG”
Chief Of The Gastroenterology, Hepatology And Nutrition At The University Of Chicago

The mainstay of treating a food allergy remains simple:

You must completely eliminate the offending food. The involvement of a dietitian can be of major help in managing your new diet, and help with tasks like label reading, dining out, and maintaining nutrition without allergens. 

In addition, those who suffer from severe food allergic reactions are also provided with an injector pen filled with doses of adrenaline (i.e. an EpiPen) that is meant to be used immediately upon a possible exposure to the offending food.

Some allergies - most commonly milk, egg, wheat, and soy allergies can resolve in children as they age. A board-certified allergy specialist can work with you to do regular testing and oral food challenges as necessary. 

Recently, specific treatment plans aimed towards growing out of the allergy (desensitization) have been developed and can be used under strict medical supervision: they consist of repeated exposures to minuscule but increasing doses of the offending food (Oral Immunotherapy or OIT)

What is a food intolerance?

A food intolerance, or what some may call a food sensitivity, causes the body to have difficulty digesting and/or absorbing specific foods.

 Symptoms of a food intolerance often include:

In practical terms, the main difference between the symptoms with an intolerance and an allergy is that with food allergies, even a small intake of the offending food will cause a reaction. On the other hand, if you are intolerant to specific foods, you probably won't see any visible signs right away after you eat, and rather larger amounts of the questionable food are needed before a reaction ensues. Symptoms of food intolerance take usually longer to develop and you may not realize that there is a problem for hours or days.

Causes of food intolerance

There are several causes of food intolerance. The most common factor is the absence or the reduced activity of enzymes needed to digest foods which in turn will cause improper digestion and absorption. Almost all foods require enzymes to break them down. With a lack of appropriate enzymes, the digestive tract will be unable to break down foods and cause bowel issues (i.e., gas, bloating, diarrhea, headaches). 

A well-known example of this is lactose intolerance, where your body lacks enough amounts of the lactase enzyme to properly break down lactose in the intestinal loops, and so this sugar remains intact and as such cannot be absorbed and causes symptoms. 

Lactose intolerance is very common in the adult population of North America. In fact, a large part of the population is genetically pre-programmed to lose their lactase activity after a certain age (usually not before the age of 8-9) and thus becoming lactose intolerant. It should be remembered that if you happen to be lactose intolerant, ingesting lactose will cause symptoms (depending on the amount ingested) that are always transient, until your body gets rid of the lactose, and will not result in any inflammation or permanent damage. For conditions like lactose intolerance, a lactose-specific digestive enzyme taken with a meal can help break down the lactose.

Other conditions of food intolerance include:

  • FODMAPs (a group of sugars present in many vegetables and resistant to digestion that might cause bowel disturbances)
  • Caffeine hypersensitivity
  • Sulfite sensitivity
  • Sucrose intolerance
  • Fructose intolerance
  • Food colorings and food additives
  • Sugar alcohols

What about wheat or gluten intolerance?

The issue with wheat is more complex. Aside from celiac disease, an autoimmune disease affecting about 1% of the North American population, in the past decade, much attention has been dedicated to another condition apparently also related to gluten ingestion. This is what we call ‘Non-celiac gluten sensitivity’ or ‘Non-celiac wheat sensitivity’. 

In reality, it is not clear whether gluten or wheat (with its other proteins or carbohydrates) is responsible for this condition that affects exclusively adults. Many studies have failed to show what is actually responsible for this intolerance. Since there are no biomarkers for this condition, no laboratory test and no doctor can positively confirm the diagnosis. Thankfully, it appears that this vague, and ill-defined condition does not really carry any long-term consequences - unlike celiac disease or food allergies.

In any case, if you suspect an intolerance to wheat, please consider being tested and seeking medical advice before beginning a gluten-free diet.

Food intolerance treatment

There are many other types of food intolerances/sensitivities that may require more than just a pill. A board certified allergist can work with you to determine that you don’t have a food allergy, and then work with you to better understand your intolerances. You may be asked to temporarily eliminate certain groups of foods from your diet (aka an elimination diet), and strategically reintroduce them to see if they are problematic. 


There are a few important differences between a food allergy and food intolerance you should be aware of. Food allergies originate from an immune reaction, while intolerances involve the digestive system; an intolerance cannot be life-threatening; but a food allergy can be. 

Food allergy reactions happen quickly and can be triggered by minute amounts of the offending food, while food intolerances typically require larger amounts and may take hours to days to manifest. While a food intolerance will cause some irritable pain in the abdominal area, it will not cause severe reactions such as anaphylaxis. 

And lastly, only for some intolerances are tests available (e.g. for lactose or fructose intolerance), so determining if one suffers from food intolerance it’s often more of a process of elimination - guided by an expert like a dietitian. Instead, food allergy tests  are available but since many on the market are unreliable and even the IgE-based are not always telling the whole story and might be misleading, their choice and interpretation must be guided by an expert like a board-certified allergist or gastroenterologist.

Updated on
August 11, 2022
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