Food Allergy vs. Food Sensitivity: Understanding the Difference

A food allergy is an immune reaction driven by an antibody called IgE. It usually starts within minutes to a few hours and can be serious. A food sensitivity is a slower immune response that researchers link to a different antibody, IgG. A food intolerance, like lactose intolerance, is a digestive problem that doesn't involve the immune system.

If you're sorting out food allergy vs. food sensitivity, the key questions are which part of your body is reacting and how fast. Below, we compare all three side by side, explain what IgG vs. IgE can and can't tell you, and show where intolerances fit.

Food Allergy vs. Food Sensitivity vs. Intolerance: What's the Difference?

The difference between a food intolerance vs. allergy vs. sensitivity comes down to what's driving the reaction: IgE antibodies (allergy), IgG antibodies (sensitivity), or digestion (intolerance). Timing, symptoms, and severity follow from that.

Symptoms can overlap, especially digestive ones, which is why these three are so easy to mix up.

If a reaction is severe, get emergency care. Swelling of the lips, tongue, or throat, trouble breathing, wheezing, dizziness, or fainting after eating can be signs of anaphylaxis. Call 911 or your local emergency number right away. An at-home test isn't designed to help with this.

Food allergies: What is IgE, and What Does it Tell You?

IgE is the antibody behind classic food allergies. An IgE result shows whether your immune system is primed to react to a food, but on its own it doesn't confirm an allergy.

Food allergens are usually proteins in a food that your immune system recognizes and reacts to. In an IgE allergy, that reaction tends to be quick. It can affect the skin, eyes, breathing, gut, and heart.

IgE testing is standard clinical practice. Allergists use skin prick tests and IgE blood tests to help identify which foods may be behind a reaction. A few points matter here:

• IgE alone isn't an allergy. You can carry IgE to a food and eat it with no symptoms. Doctors call this sensitization. A true allergy needs both the IgE and a reaction when you eat the food.
• Suspected allergies often aren't. U.S. allergy guidelines note that 50 to 90 percent of presumed food allergies turn out not to be allergies after all.
• A higher number doesn't mean a worse reaction. IgE levels can't reliably predict how severe a reaction would be.
• A physician confirms it. An allergist pairs your history with testing and, when needed, a supervised food challenge.

For these reasons, any IgE result, from any test, should go to a physician before you change what you eat.

Food sensitivities: What is IgG, and What Does it Tell You?

IgG is the most common antibody in your blood. An IgG food result shows that your immune system has responded to that food. Allergy experts see it mainly as a sign you've eaten that food, and some researchers are studying whether it also relates to symptoms.

Here's what's well established, and what's still open:

IgG to foods is common. Even people with no food problems have IgG to foods they eat. Allergy experts see it as a marker of exposure to a food, and even tolerance of it.

Allergy groups don't use it to diagnose. Allergy organizations in Europe, the U.S., and Canada advise against using IgG to diagnose food allergy or intolerance.

IgG can't rule out an allergy. A person with a true IgE allergy may not have high IgG to that food.

Some researchers see more to it. They describe a delayed, IgG-linked response, with symptoms showing up roughly 8 to 72 hours after eating. That delay makes it hard to connect symptoms to a food. The same authors note the idea remains controversial.

Trial results are early but encouraging. In two trials of people with IBS, one group cut the foods their IgG test flagged, and the other cut different foods for comparison. While the first group did better, authors say more research is worthwhile.

So how should you use an IgG result? Think of it as a list of foods your immune system has responded to. This is a helpful starting point for a careful food trial with your healthcare provider, but it isn't a diagnosis.

Where Do Food Intolerances Fit?

Intolerances aren't immune reactions, so no antibody test, IgE or IgG, can measure them.

In the case of lactose intolerance, for example, your small intestine makes too little lactase, which is the enzyme that breaks down lactose, the natural sugar in milk. Undigested lactose moves into the colon, where bacteria break it down and create gas and fluid.

This can lead to symptoms like bloating, gas, diarrhea, nausea, stomach pain, and/or stomach rumbling, which can start within a few hours of having dairy. They may be mild or strong, depending on how much lactose you have. Most people with lactose intolerance can handle some lactose without symptoms.

To check for lactose intolerance, a doctor will review your symptoms and history and may use a hydrogen breath test.

A note on food sensitivity vs. intolerance: both can bring digestive symptoms, an overlap that causes plenty of confusion. The difference is whether your immune system is involved. A sensitivity is an immune response, while an intolerance is a digestion issue.

Example: Dairy Allergy vs. Lactose Intolerance

A dairy (milk) allergy and lactose intolerance both start with milk, but they involve different parts of it. A milk allergy is your immune system reacting to the proteins in milk, while lactose intolerance is your body having trouble digesting milk’s natural sugar.

Can you have both? Yes, it's possible to have both a milk allergy and lactose intolerance. In some people, especially young children, a milk allergy can affect the small intestine enough to lower lactase, so the symptoms of both overlap. That's another reason to work with a doctor instead of guessing.

Why Does Looking at Both IgE and IgG Matter?

IgE and IgG are separate pathways, so a result on one can’t stand in for the other. Looking at both gives you a fuller picture of which foods your immune system reacts to. Keep in mind:

• They can show up together. Studies have found people with both IgE and IgG to the same foods.
• A normal IgG result doesn't rule out an allergy. Someone with a true IgE allergy may not have high IgG to that food.
• Many tests check just one. Many food sensitivity tests on the market look only at IgG.

That's the idea behind Viome's Food Allergy & Sensitivity Test. It lets you stop guessing and understand which foods your immune system reacts to, through IgE, IgG, or both.

The test checks 107 foods for both allergy (IgE) and sensitivity (IgG), all from one finger prick. Samples are analyzed in Viome’s own CLIA-certified lab, and results are physician-reviewed.

FAQs

What's the difference between IgG and IgE?

IgE is the antibody behind food allergies, which usually react fast and can be serious. IgG is the most common antibody in your blood, and some researchers link it to slower food sensitivities. IgE testing is standard in allergy care, while the meaning of food-specific IgG is still being studied.

Is a food sensitivity the same as a food intolerance?

No, a food sensitivity involves an immune response, while an intolerance is a digestion problem, like not having enough lactase to break down milk sugar. Both can come with digestive symptoms, so it's worth working with your healthcare provider to sort out which is which.

Can you have a food allergy and a food sensitivity at the same time?

Yes, you can have a food allergy and a food sensitivity at once. IgE and IgG are separate pathways, and studies have found both in the same people. A normal IgG result also doesn't rule out an IgE allergy.

Which type of test do I need?

If you react quickly or strongly to a food, see an allergist, who will combine your history with IgE testing and sometimes a supervised food challenge. If your symptoms are slower or harder to pin down, a test that looks at both IgE and IgG can show which foods your immune system reacts to, as a starting point to discuss with your healthcare provider. If you suspect lactose intolerance, ask your doctor about a hydrogen breath test.

Can an at-home test diagnose a food allergy?

No, a physician confirms an allergy using your history and other tests, while an at-home test can show which foods your immune system reacts to. That matters, because many suspected food allergies turn out not to be actual allergies.

Why would a food I eat often show an IgG response?

IgG to foods is common in healthy people and often reflects foods you eat regularly. That's why an IgG result is best treated as a starting point, not a diagnosis.

References

1. Atkinson, W., Sheldon, T. A., Shaath, N., et al. (2004). Gut, 53(10), 1459–1464. https://gut.bmj.com/content/53/10/1459
2. Boyce, J. A., Assa'ad, A., Burks, A. W., et al. (2010). Journal of Allergy and Clinical Immunology, 126(6), 1105–1118. https://www.jacionline.org/article/S0091-6749(10)01569-1/fulltext
3. Carr, S., Chan, E., Lavine, E., et al. (2012). Allergy, Asthma & Clinical Immunology, 8, Article 12. https://link.springer.com/article/10.1186/1710-1492-8-12
4. Darma, A., Sumitro, K. R., Jo, J., et al. (2024). Nutrients, 16(3), Article 414. https://www.mdpi.com/2072-6643/16/3/414
5. Gałęcka, M., Szachta, P., Bartnicka, A., et al. (2013). Gastroenterology Review/Przegląd Gastroenterologiczny, 8(4), 225–229. https://www.termedia.pl/IgG-dependent-allergy-and-selected-gastrointestinal-diseases,41,21372,1,1.html
6. Gocki, J., & Bartuzi, Z. (2016). Advances in Dermatology and Allergology/Postępy Dermatologii i Alergologii, 33(4), 253–256. https://www.termedia.pl/Role-of-immunoglobulin-G-antibodies-in-diagnosis-of-food-allergy,7,28099,1,1.html
7. Lemons, L. (2022, November 15). Allergy Insider. Thermo Fisher Scientific. https://www.thermofisher.com/allergy/us/en/living-with-allergies/food-allergies/food-sensitivity-test-vs-food-allergy-test.html
8. National Institute of Allergy and Infectious Diseases. (2011). (NIH Publication No. 11-7699). https://www.niaid.nih.gov/sites/default/files/faguidelinespatient.pdf
9. National Institute of Diabetes and Digestive and Kidney Diseases. (2018a, February). https://www.niddk.nih.gov/health-information/digestive-diseases/lactose-intolerance/definition-facts
10. National Institute of Diabetes and Digestive and Kidney Diseases. (2018b, February). https://www.niddk.nih.gov/health-information/digestive-diseases/lactose-intolerance/diagnosis
11. National Institute of Diabetes and Digestive and Kidney Diseases. (2018c, February). https://www.niddk.nih.gov/health-information/digestive-diseases/lactose-intolerance/symptoms-causes
12. Singh, P., Chey, W. D., Takakura, W., et al. (2025). Gastroenterology, 168(6), 1128–1136.e4. https://www.gastrojournal.org/article/S0016-5085(25)00328-2/fulltext
13. Vidarsson, G., Dekkers, G., & Rispens, T. (2014). Frontiers in Immunology, 5, Article 520. https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2014.00520/full