Testing

IgE, IgG and IgA Explained

Food intolerance reactions can be confusing, especially when symptoms are delayed or when standard allergy tests come back negative. Here’s a simple guide to what the different antibody tests mean.

IgE‑mediated food allergy (the “classic” allergy)

IgE allergies are the ones most people recognise. When someone with an IgE allergy eats a trigger food, or is exposed to an airborne alergen, their immune system releases histamine, causing symptoms that appear quickly — usually within minutes to two hours.

Common symptoms include:

• Hives or itching
• Swelling
• Wheezing or coughing
• Sneezing or congestion
• Vomiting
• In severe cases, anaphylaxis

These allergies are detected using skin prick tests or IgE blood tests.

IgG and IgA: Not true allergies, but often linked to food reactions

IgG responses are from another arm of the immune system, are often termed as 'food intolerances', and can cause a delayed reaction to a food. Reactions can occur within the 72 hours (3 days) after eating the food. This makes them much harder to detect without testing.

IgG antibodies elevated in the blood indicate an immune reaction to a food. Thus, IgG testing can help to guide elimination diets, especially when dealing with long‑standing symptoms such as:

• Abdominal discomfort
• Flatulance
• Bloating
• Headaches
• Brain fog
• Skin flare‑ups

These reactions are not dangerous, but they can significantly affect quality of life.

IgA is the main antibody in the digestive tract. Its job is to protect the gut lining and support healthy immune function.

IgA itself does not cause food allergies. However, changes in IgA levels can sometimes be seen in people with gut‑related food sensitivities, which may lead to symptoms such as:

• Nausea
• Diarrhea
• Abdominal discomfort
• Issues with nutrient absorption

These reactions tend to be delayed, appearing hours or even days after eating the food. 

Why delayed reactions are harder to identify

Unlike IgE allergies, delayed food reactions don’t follow a predictable pattern. Symptoms may build slowly, vary from day to day, or be influenced by stress, gut health or other foods eaten at the same time. This makes them more challenging to pinpoint without a structured elimination plan.

Many people only realise how much certain foods were affecting them after removing them from their diet.

Choosing the right test for your particular case and symptoms is important. 

You don’t need to be a current patient to discuss food testing options with us. If you’d like guidance on which test may be suitable for your situation, please complete our Contact Us form and our team will be in touch.