Food Allergy vs Sensitivity: What’s the Difference?

People around a table sharing pizza

You’re out to dinner at an Italian restaurant. After taking your order, your server asks: “Do you have any allergies?” You don’t know what to say because you know that after you eat that sublime quattro formaggi pizza you’ll probably feel a little bloated, sluggish and maybe constipated for the next few days. 

But that’s not an ‘allergy’… right? You won’t suddenly break out in a rash or feel your throat close up, so you say “no” and enjoy your pizza and suffer the consequences later. 

You wonder: am I allergic to this food, or am I just sensitive? Should I avoid it completely, or can I eat small amounts once in a while?

We often hear the words allergy, intolerance, and sensitivity used interchangeably to discuss your body’s response to food, but they actually mean different things to your health care providers. 

Let’s break down the terminology and testing options out there. You will also discover how your body’s reaction to certain foods could be exacerbating other issues. 

In this post, we’ll cover the following key points:

  • The key differences between an allergy, intolerance and sensitivity
  • How the body reacts to these sensitivities (symptoms)
  • Food assessments & diagnostic tests available
  • How a food sensitivity can aggravate other issues seemingly unrelated to digestion (i.e. why it’s not only for helping with your loose stools or constipation)
  • Treatment options once you identify your intolerances and sensitivities

What Is a Food Allergy?

An allergy triggers an immune response to food known as an Immunoglobulin E-mediated reaction (IgE for short). Your body sees these foods as a threat and responds to it. An allergic reaction is usually immediate and can cause rashes, sneezing, difficulty breathing and anaphylactic shock. These are usually easier to identify because the symptoms show up right away, within 0-24 hours. They can also be life-threatening. True food allergies that involve anaphylaxis require the use of an epi-pen or antihistamine. 

Common priority allergens include:

  • Eggs
  • Milk
  • Mustard
  • Peanuts
  • Shellfish 
  • Fish
  • Sesame seeds
  • Soy
  • Sulphites
  • Tree nuts
  • Wheat and triticale

Generally, if you are allergic to the above foods, they may need to be eliminated from your diet. A person with celiac, for example, needs to avoid gluten as it can damage the small intestine, preventing absorption of essential nutrients.

What is Food Intolerance?

An intolerance does not involve an immune system reaction. It can instead be a reaction to chemicals or additives in food, or due to a deficiency in an enzyme such as lactase, which is the enzyme that breaks down lactose (sugars) in milk.

The most common intolerances are lactose and histamine. 

Symptoms of lactose intolerance include bloating, diarrhea and flatulence. 

Symptoms of histamine intolerance (i.e. red wine, cheese and tuna) may include migraines, dizziness, bowel/stomach problems, runny nose, or irritation and reddening of the skin.

What is Food Sensitivity?

A sensitivity is similar to an intolerance in that the reaction produces discomfort, but is not life-threatening and does involve the immune system. This is similar to a true allergic response, but a sensitivity is Immunoglobulin G-mediated (IgG) response as opposed to IgE-mediated as in allergy. The effects can manifest 24-72 hours after exposure, so it is sometimes referred to as a delayed hypersensitivity reaction.

Food sources that commonly trigger these reactions include dairy (milk products, cheese), eggs, wheat, gluten, and yeast. Symptoms may include IBS, headaches/migraines, fatigue, high blood pressure, eczema, asthma, joint pain, runny nose, arthritis, weight problems or fibromyalgia.


You may have heard about the tests available to help identify the ingredients that are causing harm. Here’s a list of the most common:

IgG Antibody Test

The IgG test is used to detect food sensitivities. It measures Immunoglobulin-G antibodies in the blood, indicating the severity of the response to the food. To learn more, see our page on diagnostics testing here

IgE Antibody Test

The IgE test measures Immunoglobulin-E antibodies. This test is done for food allergies (immediate, severe reactions). The higher the concentration of IgE antibodies in the blood, the more hypersensitivity to a particular food. These tests may be covered by OHIP in Ontario, if deemed medically necessary and requisitioned by a family doctor or allergist. 

Skin Prick Test

The skin prick test is most commonly used by allergists. This procedure is also covered through OHIP or medicare in Canada. A small drop of the allergen is injected in a patient’s arm or back. If the skin produces a small red bump called a wheal, this indicates an allergic reaction.

Elimination Diet

With this approach, you completely remove the food source that may be causing a reaction for at least 2-4 weeks, while being supervised by a healthcare provider such as a naturopathic doctor or registered dietitian. 

It’s Not Just Bowel Issues

Healthy gut hands on stomach
Source: Pixabay

Research shows that eliminating foods identified on these tests can improve IBS, migraines, weight gain, rheumatoid arthritis and ADHD. 

An immune-mediated response has the potential to cause inflammation, and by eliminating or reducing these foods, symptoms can improve or disappear.

There is especially promising research on the role gut health plays in mental health, considering that 95% of the body’s serotonin is produced in the gut.

To learn more about the link between nutrition and mood, check out this webinar on designing your diet for mental health by Rebecca Minshall, RD.

Treatment Options

The natural cure for a true allergy is avoidance. If you actually have a food sensitivity or intolerance (not an allergy where exposure would prompt a life-threatening response), then some try reintroducing the food after a sufficient period of time or after you’ve reduced inflammation in the gut to see if your tolerance has changed. You may notice that you can tolerate small amounts once in a while. 

True food allergies that involve anaphylaxis require the use of an epi-pen or antihistamine. For food intolerances, some try the elimination “hypoallergenic” diet, herbs, quercetin and probiotics. 

Key Takeaways

Consult with a naturopathic doctor to see if an elimination diet or IgG test is for you. A naturopathic doctor or dietitian can help you to interpret your test results and supervise an elimination diet, and guide you in creating a nutrition plan.

As you arm yourself with more information, you are taking the first steps towards resolving your digestive issues and feeling better.


Photo of Judith Lemieux contributor
Judith Lemieux, MA