Allergic or Intolerant?

Here’s the difference

Allergic or Intolerant?

If you have reactions to what you eat, sitting for a peaceful meal or lively work potluck can feel more like running an obstacle course. But are you allergic, or is it something else?

What is a food allergy?

True food allergies trigger an immune system response. Immunoglobulin E (IgE)-mediated food allergies activate the adaptive immune system, which is typically on high alert to detect and fend off potentially dangerous parasites and pathogens. (Non-IgE-mediated allergies also exist, but are less well understood. Many are believed to be T-cell-mediated.)

In the case of an IgE-mediated allergic reaction, instead of fighting off invaders, IgE binds to benign substances like food proteins. These immune system triggers are known as allergens. In terms of food allergies, contact usually occurs through eating, but skin exposure or inhalation of food residue may also activate a response.


Allergen binding causes the release of inflammatory substances that promote recognizable allergy symptoms:

  • Skin reactions (hives, rash, swelling) are the most frequent symptoms associated with IgE-mediated food allergies and occur in 80 percent of allergic reactions.
  • Gastrointestinal symptoms include nausea, vomiting, diarrhea and abdominal pain.
  • Respiratory problems may include itchy and runny nose, sneezing, spasms in vocal chords and wheezing, as well as itchy palate and swelling of lips or tongue.
  • Low blood pressure may cause dizziness and/or fainting.
  • In severe instances, anaphylactic reactions to an allergen may have fatal consequences.

To be classified as an IgE-mediated response to a food, symptoms must occur within two hours of exposure.

Common allergens

In adults, the most common allergens include

  • peanuts
  • tree nuts
  • seafood

If you suspect you have an allergy, consult your doctor or health care practitioner. Due to the potential danger of allergy tests, they are typically performed in a specialized clinic.

What is a food intolerance?

Rather than involving the immune system, food intolerances induce undesirable reactions to food through a variety of other mechanisms.


Food intolerances may play a role in irritable bowel syndrome, which is a chronic gastrointestinal disorder. Adverse reactions to food may also include

  • gastrointestinal symptoms
  • arthritis
  • eczema
  • headaches
  • hives
  • lethargy
  • migraine
  • respiratory symptoms
  • sneezing
  • itchy and runny nose
  • watery eyes

Unlike allergic reactions, which are usually immediate, reactions due to non-allergic sensitivities can be delayed up to several days and are often long lasting. Although a minute amount of an allergen will prompt an immune response, some people who experience food intolerances have a threshold for the offending food and can take it in small amounts; larger quantities or more frequent consumption of the food will bring about a reaction.

What causes a food intolerance?

There are many possible explanations for a food intolerance. Reactions could occur due to a deficiency in an enzyme required to break down the trigger food, which is what occurs in the case of lactose (milk sugar) intolerance. In cases of lactose intolerance, gastrointestinal responses are common and include bloating, cramps, diarrhea and flatulence.

Overconsumption of a food or food additive can cause unpleasant consequences in some people. In other instances of food intolerance, there is as yet no explanation.

How is a food intolerance diagnosed?

Elimination diets may be the most effective—if most cumbersome—method of isolating a food culprit. Strictly avoid all suspect foods for at least two weeks to establish whether symptoms abate. Then, reintroduce one food at a time, spaced out over a few days, to determine if symptoms reappear.

Because avoiding food groups may restrict your nutrient intake, it’s best to work with a dietitian, nutritionist or naturopath to ensure you don’t become deficient.