IgE vs IgG in food allergy; Are they the same? [2024]

By Hannah Whittaker RD, PGDip | Jun 10, 2024

Allergies can be a confusing topic, especially when you find terms like IgG or IgE during a Google search. These scientific-sounding names can make it difficult to understand what’s really going on in the body.

As a dietitian specialising in food allergy I’m here to help you to demystify these terms. I’ll explain the impact both have on your little ones body, whether they can cause an immune response and what actually is the difference between IgE vs IgG.

What are Food Allergies?

Food allergies occur when the immune system reacts to substances (allergens) that are generally harmless to most people.

These reactions can involve different antibodies and when you do your Google Search I’ve found Immunoglobulin E (IgE) and Immunoglobulin G (IgG) are the most common antibodies discussed when it comes to food allergy.

It’s important though to understand that IgE and IgG antibodies are not the same and not both are related to food allergy. 

IgE vs IgG in food allergy; Are they the same?

No, they aren’t the same. IgE antibodies can be related to food allergy but IgG are not. Although this is a simple answer, there is much more to it. Read on to find out more and why

IgE Allergy Meaning

IgE (Immunoglobulin E) is an antibody that plays a crucial role in the body’s immediate allergic response.

When someone has an IgE allergy, their immune system overreacts to certain substances, called allergens.

These allergens could be things like pollen, pet hair, or food allergies such as cow’s milk, peanut or egg. 

When the allergen enters the body, it triggers the production of a specific type of antibody called Immunoglobulin E, or IgE for short. This is called an immune-mediated response. 

In an IgE reaction these IgE antibodies attach themselves to special cells in the body called mast cells. Mast cells are found in various tissues, including the skin, lungs, and gastrointestinal tract. 

Now, when the person encounters the allergen again, the allergen binds to the IgE antibodies on the surface of the mast cells. This triggers the mast cells to release chemicals (such as the release of histamines), into the surrounding body tissues. 

These chemicals that are released cause the symptoms of an allergic reaction to occur. In an IgE allergy this reaction will occur anywhere from immediately after the food is eating up to around 2 hours later. 

What are the symptoms of IgE-Mediated Food Allergy?

The symptoms of IgE allergy can vary between people and can also range from mild-moderate to more severe. Here is an example of some symptoms that may occur;

  • Hives
  • Swelling
  • Itching
  • Gastrointestinal symptoms (abdominal pain, vomiting, diarrhoea)
  • Respiratory issues (wheezing, shortness of breath)
  • In more severe cases Anaphylaxis (anaphylactic shock) may occur which is a severe, potentially life-threatening reaction to a food allergen. 
IgE vs IgG Allergy

IgE Food Allergy Testing

When it comes to diagnosis of IgE food allergy it is important that prior to this testing that a full allergy focussed history is taken. This should be done by a qualified clinician. 

Taking this history helps to ensure that the correct testing is requested.

If symptoms are delayed and not immediate it may be that your baby has another type of allergy called non IgE.

In non IgE food allergy symptoms can occur anywhere from 2-72 hours after a food is eaten, not immediately. Although the immune system is involved in this reaction there are no antibodies produced. Check out my blog on IgE vs non IgE allergy for more information.

Diagnosing IgE-mediated food allergy

There are three validated ways to diagnose IgE allergies at present. These are;  

Skin Prick Tests

In a skin prick test, a small amount of food allergen extract is placed on the skin, usually on the forearm or back. Then, a small instruments called a lancet is used to prick or scratch the skin. The health professional will wait around 15-20 minutes to check if a reaction occurs. A reaction will look like a small raise bump, called a wheal. If this wheal is larger than 3mm in diameter then this may mean a positive IgE allergy to that food. 

Blood Testing for IgE Allergy

Blood tests are another type of way to check for IgE antibodies to a food. They measure the levels of specific IgE antibodies in the bloodstream. A blood sample is taken and sent to a laboratory for analysis. The results are reported as a numerical value indicating the amount of IgE antibodies to each food allergen tested. If the IgE levels are high this is likely indicating a positive IgE allergy to that food. Higher values also typically indicate a stronger allergic response to that particular allergen.

IgE vs IgG Allergy

Oral Food Challenge

Oral food challenges (OFCs) are done under the supervision of a specialist within a hospital setting to help to diagnose or check if a child has outgrown a food allergy.

During an OFC, a child will be given the food that caused a reaction in a controlled environment. Healthcare professionals will closely monitor for any allergic reactions that may occur during the challenge. OFCs are considered the gold standard diagnostic tool because they provide direct, real-time evidence of a person’s ability to tolerate a specific food.

What are false positive allergy results?

In skin prick and blood testing we can get what is called a false positive. From research, false positives can be seen in around 50-60% of allergy testing.

False positive results can show raised IgE blood levels to a specific allergen (food) but this does not mean your little one has a food allergy.  

Why do false positives occur?

When you eat a food, your digestive system breaks down food proteins, making them less likely to trigger an allergic reaction. However, skin prick tests (SPTs) and blood tests don’t mimic digestion. They can expose your body to larger proteins, which may make it easier for IgE antibodies to detect and react to these proteins. This can make your little one seem more sensitive to a food allergen than they actually are. 

There is also the risk of cross reactivity. Some allergen foods are in the same family and can share similar proteins. For example, if you’re child has an allergy to peanuts, tests might also show a reaction to legumes because they have similar protein structure, even though legumes don’t actually cause any symptoms when they are eaten.

These test results must be interpreted by a clinician alongside a full allergy focussed history. This makes sure the correct diagnosis is made. 

IgG vs IgE Food Allergy

What is IgG?

IgG, or Immunoglobulin G , is one of the most common types of antibodies found in the blood. Antibodies are proteins that the immune system uses to identify and neutralise foreign objects like bacteria and viruses. Unlike IgE, which is involved in immediate allergic reactions as we’ve already spoken about, IgG antibodies are part of the body’s longer-term immune response.

How do IgG antibodies work?

Having IgG antibodies in your blood is often a normal response and not necessarily a sign of food allergy. 

If you have a low level of total IgG antibodies, this may mean that your immune system is a little low.  When low, IgG antibodies may not work as well and this can impact on the body’s defense system. This can affect the sinus cavities, the nose and throat and digestive system. 

If your levels of IgG antibodies are low a lot of the time then you may need antibiotics to support your immune system.

Symptoms of IgG Reactions

In some studies raised levels of IgG antibodies have been linked to the below symptoms. These include;

  • Skin problems such as; Rashes, hives, and asthma. 
  • Gastrointestinal issues like abdominal cramps, diarrhea, and constipation and symptoms of irritable bowel syndrome. Lactose intolerance may also be linked to raised IgG antibodies. 
  • Joint pain

Raised IgG antibodies have also been linked to inflammation in the body.

The Reality Behind Food Sensitivity Testing for IgG 

You will probably find IgG tests available online that claim to be able to diagnose allergy to a specific food by checking IgG antibody levels.

It’s important to note that IgG tests have not been scientifically proven to deliver on these claims and there is a lack of evidence to support this. 

The studies supporting these food sensitivity tests using IgG antibodies are often outdated and published in non-reputable journals. 

The presence of IgG antibodies is likely a normal response of the immune system to that food exposure. In simpler terms, your little one has eaten the food that has appeared positive on the allergy test results.

IgG Allergy Testing – Expert Opinion

Due to the lack of scientific evidence supporting IgG testing in diagnosing food allergy, many reputable organisations advise against its use for diagnosing food allergies, intolerances or sensitivities.

These include the American Academy of Allergy, Asthma & Immunology, the British Dietetic Association, and the Canadian Society of Allergy and Clinical Immunology and me as an expert food allergy dietitian. 

Seeking Reliable Advice on IgE vs IgE allergy.

While it’s natural to seek non-medicinal ways to feel better, it’s crucial to base your decisions on proven and reliable advice. Especially when it comes to a childs’ health.

As a parent, it’s important to approach food allergy testing for your little one with caution, especially when considering methods such as food IgG tests.  My message to you, DON’T WASTE YOUR MONEY!

While these tests may seem like a straightforward solution, it’s crucial to understand that they aren’t validated tools for diagnosing food allergies in children. Relying solely on the results of such tests can lead to unnecessary dietary restrictions and advice on following an elimination diet that could be potentially harmful. 

Following restrictive diets without proper guidance from healthcare professionals could also contribute to disordered eating habits and nutrient deficiencies in your little one. 

To ensure the best for your child, it’s essential to seek evidence-based advice from qualified healthcare providers, such as myself. 

Summary – IgE vs IgE allergy; What’s the difference? 

Understanding the difference between IgE and IgG is crucial when it comes to food allergy. 

Remember IgE antibodies are behind those immediate allergic reactions, happening anywhere from immediate to 2 hours after the food is eaten. Some symptoms of IgE allergy may be hives, swelling, tummy disburbance. In more severe responses children can experience symptoms such as difficulty breathing and anaphylaxis. 

On the other hand, IgG antibodies are part of the body’s longer-term immune response and aren’t a reliable measure to identify food allergy.  

Relying on IgG tests can lead to unnecessary dietary restrictions and potential nutrient deficiencies for your little one and you if breastfeeding you may miss out on key nutrients too.

Always seek advice from qualified healthcare providers to ensure you get the correct diagnosis. This will ensure that your childs allergies are managed correctly.

Hannah Whittaker Dietitian Bump2baby Nutrition
Expert Pregnancy & Paediatric Dietitian at  | info@bump2babynutrition.com | Website

Hannah is an Expert Registered Dietitian specialising in Vegan Family Nutrition and Cows Milk Protein Allergy. 

She is a respected figure in the field of nutrition and a captivating speaker and sought after media spokesperson being featured in esteemed publications including the Sunday Times, Independent and Huffington Post.

Credentials

Registered Dietitian
First Class Degree in Nutrition

Experience

Over 15 years experience working in the field of nutrition
Respected Media Spokesperson both in the UK & USA; quoted online, TV and in local and international news
Writer & Researcher, supporting the BDA and PEN Nutrition

 

 

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