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Food Allergy vs Intolerance vs Sensitivity: The Honest Difference (and the IgG Test Truth)

A food allergy is an immune reaction (IgE) that can be fast and, at worst, life-threatening, so it needs a doctor. A food intolerance is a non-immune reaction, usually slower and dose-dependent, that is uncomfortable but not dangerous. "Food sensitivity" is a loose, non-clinical word people use for either one. And the popular IgG food tests are not recommended for diagnosing either.

The short version. Allergy is an immune (IgE) reaction that can be fast and severe and always belongs with a doctor. Intolerance is a non-immune reaction, usually slower and dose-dependent, uncomfortable but not life-threatening. "Sensitivity" is an informal umbrella term for either. Major allergy bodies advise against IgG or IgG4 food-panel tests for diagnosing food allergy or intolerance, because a positive result more likely reflects normal exposure than a problem food. Any sign of a severe allergic reaction, such as trouble breathing or swelling of the lips, tongue, or throat, is an emergency.

If you have searched "is the IgG food test legit" or "I tested positive for everything," you are in the right place. This page explains the three terms plainly, shows the allergy red flags that always mean see a doctor, and tells you honestly what the IgG evidence says.

The one-sentence version of each

  • Food allergy is your immune system reacting, specifically with IgE antibodies, to a food it has mistaken for a threat. It can come on within minutes and can be severe (NHS, food allergy; AAAAI, food allergy).
  • Food intolerance is not an immune reaction. It is usually a problem digesting or processing a food, such as lactose (an enzyme issue) or histamine (a metabolic and fermentation issue). It tends to be slower and depends on how much you eat (NHS, food intolerance; British Dietetic Association).
  • Food sensitivity is not a precise medical term. People use it for both of the above, and sometimes for things that are neither. Because it means different things to different people, it is worth being careful with it.

That ambiguity matters. When someone says "I have a food sensitivity," they might mean a true allergy, a lactose problem, a histamine pattern, or just a food that does not agree with them. The word alone does not tell you which, and the safe response depends entirely on which it is.

The comparison table

Food allergyFood intolerance
MechanismImmune system, IgE-mediatedNon-immune: enzyme (lactose) or metabolic and fermentation (histamine)
OnsetOften fast, within minutes to a couple of hoursOften delayed, hours to the next day
Dose-dependenceA tiny amount can trigger a reactionUsually dose-dependent: a little may be fine, a lot is not
SeverityCan be life-threatening (anaphylaxis)Uncomfortable, not life-threatening
DiagnosisAllergist, clinical testing (IgE)Pattern over time plus supervised elimination and reintroduction

Sources: NHS, AAAAI, British Dietetic Association.

Allergy red flags: seek urgent medical care. If you or someone else has trouble breathing, swelling of the lips, tongue, throat, or face, a tight throat, sudden dizziness or faintness, or a feeling of collapse after eating, treat it as an emergency and get medical help immediately. These can be signs of anaphylaxis, a severe allergic reaction (NHS, food allergy). Suspected allergy always belongs with a doctor, not with an app and not with a self-test. A doctor's appointment is NOT the right response here.

Why the difference is not just semantics

The mechanism changes everything about what you should do.

With a true allergy, the amount barely matters. A trace can set off a reaction, and the reaction can escalate fast. That is why allergy is a doctor's job, diagnosed by an allergist using IgE testing and your history, and why an EpiPen exists. Guessing is not safe here.

With an intolerance, the picture is the opposite in two ways. It is usually slower, and it usually depends on dose. Many people with lactose intolerance handle a splash of milk in coffee but not a glass of it. Many people with a histamine pattern handle one glass of wine but not wine plus aged cheese plus leftovers in the same day. The reaction may also arrive hours later, which is exactly why the last thing you ate is so often the wrong suspect.

So allergy is about avoiding a trigger completely under medical guidance. Intolerance is about finding your personal threshold, usually through careful observation and a supervised elimination-and-reintroduction trial, not a one-off test.

Coeliac disease is a third thing

Coeliac disease is neither a classic allergy nor a simple intolerance. It is an autoimmune condition: eating gluten triggers your immune system to attack your own gut lining (Coeliac UK; NICE). It is diagnosed with specific blood tests and usually a biopsy, and it is important to get tested before cutting out gluten, because removing gluten first can hide the disease and make diagnosis harder.

A related term, "non-coeliac gluten sensitivity," is genuinely contested. Some people report symptoms from gluten-containing foods without coeliac disease or a wheat allergy, but the mechanism, and even whether gluten itself is the trigger, is not settled in the research. We say that plainly rather than overstate it. If gluten seems to be a problem for you, get coeliac disease ruled out first by a clinician.

The IgG / IgG4 food test truth

This is the question that brings most people to this page. The short, sourced answer: IgG and IgG4 "food sensitivity" panels are not recommended for diagnosing food allergy or food intolerance.

Here is why, from the people whose job is to set the standard. The European Academy of Allergy and Clinical Immunology reviewed the evidence and concluded that testing for IgG4 against foods is not recommended as a diagnostic tool (EAACI Task Force, Stapel et al., Allergy 2008, PubMed 18489614). Their reasoning is the part worth understanding: IgG4 to a food is a normal response to eating that food. It reflects exposure and, if anything, developing tolerance, not intolerance. A positive result is closer to "you eat this" than to "this harms you." That is why a panel can come back flagging foods you eat often and tolerate perfectly well.

The American Academy of Allergy, Asthma and Immunology agrees, in published support of the EAACI position (AAAAI, JACI 2010) and in its Choosing Wisely guidance, which advises against using IgG tests to diagnose food allergy or intolerance. The British Society for Allergy and Clinical Immunology says the same in its Choosing Wisely statement on alternative tests (BSACI, 2020).

We are not calling these tests a scam. We are pointing you at the position statements from the bodies that define the field and letting the facts stand. The risk is practical: a positive panel can lead someone to cut out many foods they were tolerating fine, which narrows the diet for no real benefit and can create anxiety around eating. If you tested positive for almost everything, that is a known feature of how these tests behave, not a sign that you are allergic to your whole fridge.

So how do you actually find a food problem?

For suspected allergy: see a doctor or an allergist. Do not experiment. The red flags above are not negotiable.

For suspected intolerance: the honest method is unglamorous but it works better than any single panel. You watch for patterns over time, accounting for dose, then you confirm with a supervised elimination-and-reintroduction trial, ideally with a dietitian (British Dietetic Association). The hard part is that intolerance is about dose and timing across days, which is genuinely difficult to track in your head, especially when reactions are delayed.

How GIMETRY fits (honestly)

GIMETRY does not diagnose allergy or intolerance. No app can, and a suspected allergy always goes to a doctor.

Because intolerance is usually about dose and pattern over time, this is where structured tracking helps. GIMETRY lets you log what you eat and how you feel, then compares those across different time windows to surface foods that line up with your symptoms more than chance would suggest. The output is a short list of suspects worth testing and a record you can bring to a clinician for that supervised elimination trial. It is suspects, not a verdict. It does not tell you that you have an allergy or an intolerance, and it never replaces a doctor.

If you want to spot these dose-and-time patterns in your own logs, that is exactly what GIMETRY is built to do. It will not diagnose you, and anything that looks like an allergy still needs a doctor, but it can turn a vague "something I eat bothers me" into a short, concrete list to investigate.

Not sure which one you are dealing with? Our free, 2-minute allergy-vs-intolerance explainer walks you through the differences and points you toward the right next step. It does not diagnose anything, and it always routes suspected allergy to a doctor. It is just a clearer starting point.

Frequently asked questions

What is the difference between a food allergy and a food intolerance? An allergy is an immune (IgE) reaction that can be fast and severe and is diagnosed by an allergist. An intolerance is a non-immune reaction, usually slower and dose-dependent, that is uncomfortable but not dangerous (NHS; AAAAI).

What does "food sensitivity" mean? It is not a precise clinical term. People use it loosely for both allergy and intolerance, and sometimes for neither. Because it is ambiguous, it is worth clarifying which you actually mean.

Are IgG or IgG4 food tests reliable for diagnosing intolerance? No. They are not recommended for diagnosing food allergy or intolerance. A positive IgG/IgG4 result generally reflects exposure and tolerance to a food, not intolerance (EAACI, Stapel et al. 2008; AAAAI 2010; BSACI).

Why did my IgG test flag foods I eat all the time? Because IgG4 to a food is a normal response to eating that food. It reflects exposure, so it often flags exactly the foods you eat most (EAACI, Stapel et al. 2008).

Is coeliac disease an allergy or an intolerance? Neither. It is an autoimmune condition triggered by gluten, diagnosed with specific blood tests and usually a biopsy. Get tested before cutting out gluten, because removing it first can hide the disease (Coeliac UK; NICE).

Is non-coeliac gluten sensitivity real? It is contested. Some people report symptoms without coeliac disease or wheat allergy, but the mechanism, and whether gluten is even the trigger, is not settled. Rule out coeliac disease with a clinician first.

When should I see a doctor instead of tracking food? Any sign of an allergic reaction, especially trouble breathing, swelling of the lips, tongue, or throat, faintness, or collapse, is an emergency, get medical help immediately (NHS). Any suspected allergy belongs with a doctor.

Does GIMETRY tell me if I have an allergy or intolerance? No. It does not diagnose. It compares what you eat against how you feel over time to surface suspects worth discussing with a clinician. Suspected allergy always goes to a doctor.

Sources

How this was written. This article was drafted with AI assistance and reviewed by the GIMETRY editorial team for accuracy against the cited sources. Last reviewed: 2026-06-28. GIMETRY is not a medical device and does not provide medical advice, diagnosis, or treatment. It surfaces possible patterns to discuss with a qualified clinician; it does not identify the cause of your symptoms. Suspected food allergy is a medical matter: always see a doctor, and treat the red flags above as an emergency.