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Allergies, Sensitivities & Intolerances: What's the Difference?

Updated: Nov 12, 2022

Allergies are on the rise. Life threatening reactions resulting from food allergy increased in the US by 380 percent between 2007 and 2016. (1)

Reports of reactions to food range from 5 to 38% of the population! Then there are environmental triggers, which would boost it even higher. (2, 3)

The higher reported levels likely include self-reported reactions (rather than doctor-diagnosed) and lump food allergy, intolerance & sensitivity reactions together. But, if over one third of the population has a negative reaction to a food, we should find this extremely alarming!

Allergic reaction to nuts

So, what's the difference between the three types of reactions?

How do you know if you have a true allergy or a sensitivity reaction?

Which is more likely to have a life long impact and which can be improved with treatment and gut healing?

And, why can it sometimes be so challenging to identify the offending substance?

For the answers, read on. However if you'd like a quick visual, skip to the bottom of this page for a bonus chart illustrating the top differences.

What is a food allergy?

With a true allergy, the immune system decides for some reason that a particular substance is a threat and releases IgE antibodies to counter this.

Antibodies (also called immunoglobulins - Ig for short) are large Y-shaped proteins that are found in our blood. They are a key component of our immune system as they can recognize and combine with substances in our blood that are considered foreign or alien, such as bacteria, viruses and food proteins.

A release of IgE type antibodies occurs in someone who is "allergic" every time the person comes in contact with the substance or allergen.

The reaction is usually immediate, within a few seconds to a couple of hours and can occur to even a minute amount of the food.

The IgE antibodies trigger mast cells, which line the surface of the body under the skin and internally around major organs, to release inflammatory chemicals including histamine. These chemicals cause the symptoms of allergic reactions, such as itchy skin and swelling.

Anaphylactic reaction

Allergic reactions can be life threatening! Swelling of the bronchial tubes in the lungs can interfere with breathing. A sudden drop in blood pressure can also occur due to the swelling of blood vessels. Respiratory symptoms or signs of collapse are indicative of anaphylaxis and must be treated immediately with an injection of adrenaline into muscle.

Common symptoms of an IgE mediated response include: wheezing, swelling, trouble breathing, anaphylaxis, hives, vomiting, diarrhea, stomach pain and trouble swallowing.

What is a food sensitivity?

A food sensitivity or hypersensitivity also involves an immune reaction to a food, however, it is not IgE antibody mediated. Other antibodies are involved (IgG, IgA, IgM, IgD), along with immune complexes and T cell responses.

The immune response can lead to inflammation and tissue damage, though it is not as severe or immediate as in an IgE mediated allergy reaction. The degree and severity of symptoms vary greatly because of the genetic makeup of the individual.

IgG mediated responses are thought to be the most common sensitivity reactions. With a longer half life, IgG antibodies tend to stick around longer than traditional IgE reactions. This means the response can be delayed and symptoms can take anywhere from 3 to 72 hours after exposure to manifest.

The delayed response makes sensitivities difficult to identify without a test. Which is why elimination challenges are often recommended.

Blood lab testing

IgG blood testing of around 90 to 120 foods is possible through a number of functional medicine labs. Many of these labs reside in the US, but testing is available through these labs in NZ and other parts of the world. (You can read more about Allergy & Sensitivity Testing here. It looks at the advantages & disadvantages of each).

The significance of elevated IgG levels in the blood to a particular food is hotly debated.

An IgG response is thought to occur after a meal and is considered a normal, expected reaction. (4)

The question is if elevated levels are normal. Levels are thought to decline quickly after exposure in healthy subjects, but in IgG testing they have been found to be elevated even after avoidance of a food in sensitive individuals.

The medical community believe IgG testing offers little benefit & that elevated levels simply indicate the presence of exposure and tolerance to a food. (If you've had any blood tests for food allergies through the medical system, it is likely to have only assessed IgE reactions).

Functional medicine and integrative health practitioners, however, do see value in testing IgG as an indicator of a food sensitivity. (Particularly if the test includes complement C3d, total IgG and IgG4).

A number of clinical studies have shown that elimination of IgG-positive foods can improve symptoms, including those with irritable bowel syndrome, autism, cystic fibrosis, and rheumatoid arthritis. (5, 6, 7, 8, 9, 10, 11)

Sensitivity symptoms are usually more subtle than an IgE allergy but can include:

Woman with a headache
  • Mood changes

  • Anxiety

  • Depression

  • Headaches

  • Hyperactivity

  • Nausea

  • Bloating / Gas

  • Diarrhea

  • Constipation

  • Acid reflux

  • Joint aches

  • Fatigue

  • Dark circles under the eyes

  • Weakness

  • Brain fog / Memory issues

  • Acne / Skin issues

Increased intake or frequency of consumption of a "sensitive" food is more likely to result in symptoms.

Fortunately, sensitivities can be improved with treatment and improved gut health.

What is a food intolerance?

A food intolerance is an inability to tolerate and digest a food or food group, causing an adverse physiologic response.

It can still cause low-grade inflammation and tissue damage, but an immunologic response is not elicited.

A food intolerance is usually due to a break down in gut or enzyme function, and the reaction is dose dependent. Symptoms only eventuate once your personal threshold is reached, making it difficult to determine the offending food.

For example, one day, you may eat a tomato with no issue and a few days later after eating a whole bowl of tomato soup, potato chips and avocado on toast your threshold for salicylate containing foods is blown and your body breaks out in hives!

Symptoms of a food intolerance are not immediately life threatening, but can range from mild to severe.

They can include bloating, diarrhea or constipation, brain fog, skin rashes, stomach cramps and gas. Hives, itchy nose or eyes, blocked or runny nose, eczema, sinusitis can also occur.

Common food intolerances are to:

  • gluten (found in wheat, barley & rye products),

  • lactose milk sugar in dairy (low lactase enzyme),

  • high histamine foods (like red wine, aged cheeses, fermented foods, smoked or preserved meats and often due to low DAO enzyme),

  • nightshade plant foods (such as potato, tomato & eggplant) and

  • salicylates (high in avocado, tomatoes, berries and more).

Intolerances can also occur to toxic contaminants, pharmaceuticals, and lectins (plant anti-nutrients which include nightshades, legumes & grains).

Improving gut health & aiding digestion by ensuring you have adequate stomach acid and digestive enzymes is super important when addressing food intolerances.

So, in summary...

Although the symptoms of an allergy, intolerance & sensitivity can be similar, the timing and dose response can help differentiate between them. Skin prick tests, elimination challenges, plus IgE and IgG blood testing can be also helpful.

You can read more about Allergy & Sensitivity Testing here. This article looks at the advantages & disadvantages of each.

Just a heads up though...

Unfortunately, not everyone defines these terms the same way, which causes confusion. A sensitivity is often used to describe an intolerance, and vice versa. However, myself and many in the functional medicine arena, believe differentiating them in this way makes the most sense and takes into account non-IgE mediated immune reactions.

Need help navigating the symptoms of a food allergy, intolerance or sensitivity?

See how you can work with me to get a personalized functional medicine solution.


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