Food allergies come about when someone’s immune system decides that a harmless food item is dangerous and mounts a response to that item. The response for allergies involves TH2 cell activation (a type of T cell), leading to the production of an antibody type called IgE. IgE antibody is different from IgG antibody, which is involved in responses to infections such as viral or bacterial infections. IgG is the antibody induced by vaccinations, for instance.
IgE binds to mast cells, which live in tissues like the gut, skin, and airways that are in contact with potentially dangerous substances in the environment. Mast cells contain pro-inflammatory substances such as histamine, and when activated by IgE, release them. This causes the symptoms of allergy. In the gut, these symptoms can include pain, cramping, and diarrhea, and if it becomes systemic, may also involve non-gut tissues such as the skin and airways. In serious cases, difficulty breathing, loss of consciousness, and shock can occur.
Why does the immune system think harmless foods are dangerous?
The process the immune system uses to decide if a substance is dangerous involves a kind of two-factor verification. A “sentinel cell” needs to detect that a substance is new or possibly dangerous and “present it” to a T cell — the cell that activates systemic immune responses and activates antibody-making cells. But the T cell will not respond unless the sentinel cell also presents a signal that indicates danger. These signals are induced in sentinel cells by “danger signals,” which can be pathogen products that the immune system knows can be associated with infection or be related to tissue damage.
So most basically, the food antigen is accidentally paired with a danger signal. The main hypothesis for how this comes about involves damage or disruption of one of the barriers, principally the gut, but also the airway or skin barrier (Losol 2023, Wanniang 2023), allowing the induction of the danger signal. In the case of the gut barrier, this disruption could be caused by dysbiosis, for instance due to a poor diet and/or by inflammation and stress.
Is IgE only involved in allergies?
IgE and mast cells help defend against parasites, including worms, malaria, and some diseases carried by ticks, such as Rocky Mountain Spotted Fever, Q fever, Ehrlichiosis, and others (Mukai 2016). We don’t know exactly why this system can respond to food also, but it is hypothesized that some parasites may have components that can cross-react with foods (Mukai 2016). So apparently, the immune system may be mistaking foods for parasites (!).
What’s the difference between a food allergy and a food intolerance?
Food allergies reliably invoke responses that are clearly mediated by the immune system, such as increases in IgE or hives (Hage 2025). Food sensitivities, or intolerances, occur when symptoms are generated by something other than the immune system. For instance, lactose intolerance, in which people cannot absorb dairy sugars. The unabsorbed lactose feeds microbes, which, as a consequence of their metabolism, cause gas. They also “bloom” — meaning that the colony of lactose-fermenting microbes grows — which could contribute to dysbiosis. The cause of other kinds of sensitivities or intolerances is less clear (Hage 2025). In some cases, the sensitivities may be part of irritable bowel syndrome (Soares 2018). The pathophysiology of food sensitivities is not well understood, and this complicates diagnosis and management, and has also provided lots of opportunities for “snake oil salesmen” to ply their wares.
Is there anything we can do to prevent food allergies?
A key challenge for the immune system is determining what substances are safe and should be tolerated, and which are dangerous and should be attacked or expelled. The immune system learns tolerance during infancy and early childhood (Hund 2025). It seems that exposing children to a wide variety of foods when they are young can protect against the development of food allergies, including during pregnancy and breastfeeding (Hund 2025). Diet diversity can support a healthy, diverse microbe population, which can help maintain gut barrier integrity and keep the gut immune system in a tolerant state (Han 2021).
Stress can contribute to the development of food allergies (Schreier 2014). This may be consequent to the ability of stress to increase gut barrier leakiness and thus increase the likelihood of the pairing of an innocuous food item with a danger signal, inducing an allergy. This means that addressing stress can be part of a strategy to improve allergy symptoms.