The Difference Between IgE and IgG Responses and Tests Explained


With food allergy prevalence and awareness on the rise, many people now wonder if they have food allergies and whether they should avoid certain foods for the sake of their health. Several tests can be done to detect or narrow down potential food allergens in a person’s diet. Two important diagnostic tools that are often used in the detection of food allergies and sensitivities are IgE and IgG blood testing.

IgE and IgA refer to immunoglobulins or “antibodies” and are two of the five classes of antibodies. These antibodies are produced by our bodies in an immune system response to things we have come into contact with that the body recognizes as foreign (also called antigens), such as viral cells and bacteria. These antibodies are also able to respond to other foreign matter including pollen, dust, dander and foods. Antibodies work to help the body fight against “invaders.“

What is IgE?

IgE, or immunoglobulin E, responses occur when a foreign substance enters the body by way of inhalation or ingestion of food in most cases. The IgE antibodies are most often associated with allergies. IgE allergies can cause serious symptoms including swelling, hives and difficulty breathing, and symptoms usually appear immediately. In some severe cases, IgE reactions can result in anaphylactic shock.

An IgE test is frequently performed as an initial screening procedure to detect the presence of allergies and can be done by skin prick or patch testing. This test measures how much IgE is present in a person’s blood. These antibodies are also present in the mucous membranes, lungs and skin.

IgE reactions can be treated with medications that block histamines from being released as well as avoidance of trigger foods and/or substances.

A classic allergic IgE response (Type I) occurs when a person eats a food they are allergic to. For example, when someone with a peanut allergy eats peanut, B cells in the body are exposed to the peanut allergen. These B cells then begin making IgE antibodies to bind to the allergen.

Once exposed to an allergen, IgE antibodies are able to attach to mast cells, where the antibodies wait until the next exposure to the allergen. When a person comes into contact with the same allergen again, the IgE antibodies encourage the mast cells to send out histamine and other compounds. These compounds cause symptoms most commonly associated with allergy-like inflammation and itching.

More About IgG

Antibodies associated with immunoglobulin G offer long-term resistance to infections and have a longer half-life (approximately 28 days) than IgE antibodies. With IgG allergic responses (Type III), symptoms may not occur until hours or days after a trigger food is consumed. These antibodies lead to inflammatory processes and are not associated with the release of histamines. IgG allergic or food-sensitive reactions can cause symptoms ranging from nausea and headache to hyperactivity, irritable bowel syndrome (IBS), constipation, Crohn’s Disease and excessive gas. The severity and degree of symptoms may vary depending on factors such as the genetic makeup of the person as well as the amount of repeat exposure to a certain allergen.

Although, with an IgG test, it can be difficult to pinpoint which food(s) cause problems due to a delayed appearance, an IgG test can help to narrow down the prospects.

IgG allergies are also sometimes called delayed food allergies and are often associated with digestive problems including leaky gut. Leaky gut syndrome is associated with conditions like celiac disease. When food particles enter into the bloodstream in a person who has a leaky gut, the body has an immune response and can create antibodies to fight the perceived invader. This process can contribute to the weakening of a taxed immune system.

IgG food allergies are best treated by complete elimination of problem foods from the diet.

It is important to note that with blood and skin food allergy tests, false positives and negatives can occur. A detailed oral medical history may be beneficial to have on hand to further help identify allergens when meeting with a doctor to discuss potential food allergies or sensitivities you may have.