The little-known switch that can spark food reactions

What is IgD?

IgD is one of the five main types of antibodies your immune system makes. There’s not much of it in your blood, but it’s found on the surface of developing B cells — the immune 'scout' cells that detect and respond to potential threats.

IgD helps B cells decide when to switch on and start producing antibodies. It’s also active in mucous membranes, especially in the airways, where it can help spot pathogens and trigger other immune cells (like basophils and mast cells) to release chemicals that fight infection. Even though it’s far less abundant than other antibodies like IgG or IgA, it plays an important role in monitoring for trouble and guiding how B cells respond.

FOOD REACTIONS

In terms of food sensitivities and allergies, we still have a lot to learn about IgD, but research suggests it can influence whether your immune system tolerates a food or becomes sensitised to it.

In the gut, IgD may help determine if B cells shift toward producing IgE (the antibody behind classic allergies) or toward a more tolerant response. It can also activate other immune cells, like basophils, when they encounter certain food proteins. While IgD isn’t measured in standard allergy or food sensitivity testing, it may be quietly shaping the immune 'tone' that decides whether you react to a food or not.

This could be why people react, but testing shows nothing.