Histamine May Explain IBS Symptoms

For people with irritable bowel syndrome (IBS), food is often a big trigger. Yet few people with IBS are actually allergic to the foods that cause flare-ups.^1,2

The question remains: Why are certain foods a trigger if you do not have a systemic (whole-body) allergy to them? Doctors have been trying to understand this for years. Results from a 2021 study may have uncovered an important link between histamine and IBS.^2,3

What is histamine?

Histamine is a chemical that is released by mast cells in the immune system. Your body releases histamine when you encounter an allergen.⁴

An allergen can be many different things, including specific foods. With a whole-body (systemic) food allergy, the body has a complete immune response. During this response, the immune system makes immunoglobulin E (IgE). These are antibodies that protect the body from harmful allergens.^2,4

IgE antibodies attach to mast cells and release inflammatory chemicals like histamine. This is what causes systemic symptoms of a food allergy, such as itching in the mouth, vomiting, and anaphylaxis. Food allergies can be deadly and need immediate medical care.^2,4

Local immune responses and IBS

In people with IBS, the immune system fights harmless foods, evoking a local immune response. This response is contained to one part of the intestine and can cause symptoms like stomach pain, bloating, or changes in bowel habits.^1,2

How does histamine affect IBS?

While the root cause of IBS is unknown, many people living with IBS report that their symptoms started after a gastrointestinal infection. This kind of infection is called an enteric infection. It is caused by a virus, bacteria, or parasite. An example is food poisoning. About 3 to 36 percent of new IBS diagnoses come after an enteric infection.^2,3

This has led to the theory that when the stomach encounters an infection while a certain food is present in the gut, it evokes an immune response to that food. This triggers the release of histamine, causing discomfort and pain. Whenever that food enters the body after that, the body views it as "bad." This, then, causes another local immune response, releasing histamine and causing discomfort and pain.^2,3

What did the study find?

The 2021 study tested this theory on 12 people with IBS. They were each given intestinal injections of common triggers (soy, wheat, gluten, cow’s milk). None of these people had systemic food allergies. All 12 had an intestinal local immune response.^2,3

This immune response was an IgE response linked to activated mast cells. Only 2 of 8 controls (people without IBS) had an immune response, but none of these people had symptoms.²

The takeaway message is that if you get an infection, it could affect how your body reacts to certain foods. While fighting the infection, the active immune system mistakes the food as a danger. The result is more mast cells, IgE, and histamine, which cause IBS symptoms. When the infection is gone, the body still perceives these foods as a threat.^2,3

The study shines light on the fact that allergic reactions can occur on a spectrum. While systemic allergic reactions involve the immune system and have whole-body effects, local reactions can also involve the immune system but are localized to the gut.²

Could this lead to new treatments?

According to the study, data shows that people with asthma who are treated with IgE-neutralizing drugs have fewer IBS symptoms. Data also shows that blocking histamine eases IBS symptoms.²

If IBS is linked to active mast cells and IgE release, then blocking this process could help. New drugs could be developed to stop the body from making IgE. Drugs that stop the activation of mast cells may also work.²

More research is needed

While the study shows intriguing data, only 12 people were involved. A larger study is needed, and research is ongoing. Also, there are different types of IBS. It is not known whether these results are true for all types of IBS or in people who have stress-induced IBS.^2,4

Many people with IBS have pain that doctors cannot easily diagnose. Often, IBS is a diagnosis made when nothing else "fits." This study suggests that IBS has a root cause. It could help define biomarkers to test for IBS or pave the way for new drugs.