Histamine
Histamine is a chemical compound that plays a critical role in the body's immune response, being produced and released by the immune system when it detects disease-causing pathogens or irritants. Its primary function is to neutralize perceived threats, which can trigger symptoms associated with allergic reactions when the immune system mistakenly identifies harmless substances as dangers. This release of histamine can lead to various physical symptoms, including inflammation, watery eyes, and breathing difficulties, particularly in those with allergies to substances like pollen or pet dander.
There are four identified histamine receptors (H1, H2, H3, and H4), each serving different functions throughout the body, including regulating stomach acid secretion and modulating signals in the central nervous system. Foods that are high in histamine, especially fermented or aged items, can provoke adverse reactions in sensitive individuals, potentially leading to histamine poisoning, particularly from improperly stored fish. While antihistamines can help alleviate mild allergy symptoms by blocking histamine's actions, more severe reactions require urgent medical intervention. Understanding histamine's multifaceted role is essential for addressing both its protective functions and its potential to trigger harmful allergic responses.
On this Page
Subject Terms
Histamine
Histamine is a chemical compound produced by the human body's immune system and released in response to the introduction of disease-causing pathogens or other irritants. When the immune system correctly or incorrectly identifies a foreign agent in the body as a potential threat, histamine is deployed to neutralize it. It is released and carried through the blood to the localized site of the foreign agent. Histamine affects several other brain and bodily functions by acting as a neuromodulator and neurotransmitter.
Histamine plays a major role in allergic reactions, which result when the immune system mistakes a harmless substance as a threat and deploys histamine when it is not needed. This process produces the physical symptoms of an allergic reaction. Certain foods contain high levels of naturally occurring histamine, which can cause sensitivities and allergic responses in some people. Foods with high histamine levels that are not properly stored can also cause a reaction known as histamine poisoning.
Background
The immune system is the human body's natural means of protecting itself from illnesses and infections. It is composed of a network of cells, organs, and proteins that work together to fight diseases and safeguard the body from harmful germs, or "pathogens." Apart from the central nervous system, the immune system is the most intricate feature of the human body. It has three primary functions: to destroy, remove, or otherwise neutralize pathogens such as bacteria, fungi, parasites, prions, and viruses; to detect and nullify the effects of harmful environmental irritants; and to work against the body's own cells if they become involved in disease processes such as cancer.
To achieve these objectives, the immune system functions in two main parts, known as the innate immune system and the adaptive immune system. The innate system was the first to evolve and mainly works to provide a general level of resistance against bacterial infections. Because of this, it is alternately known as the nonspecific immune system. It is mostly made up of so-called "scavenger cells," which watch out for bacteria and other pathogens, and "killer cells," which destroy them. The adaptive immune system defends the body against pathogens to which the body has been previously exposed. It mainly works to neutralize these specific pathogens by deploying proteins known as antibodies, which bind to pathogens and impede their progress or mark them for destruction by immune system cells known as macrophages.
Histamine is mainly involved in the detection and neutralization of bacterial infections and allergens. An allergen is a substance that the immune system recognizes and responds to. Common examples include pet dander, dust, and the pollen produced by plants during certain seasons. Histamine works against bacterial infections by producing low-level, localized swelling known as inflammation, which acts as a signal to other elements of the immune system and triggers them to take action to neutralize or eliminate the potentially harmful agent.
Overview
Histamine works by binding with proteins known as histamine receptors, which then act to produce a particular effect in the body. Researchers have thus far identified four specific histamine receptors, each of which plays a different role in the body. They are known as histamine H1, H2, H3, and H4 receptors. The presence and differing functions of these four receptors reveals the multifaceted role of histamine not only as an important element of the immune system but also as a neurotransmitter and neuromodulator. Histamine works in various ways to trigger signals in the brain that tell the body to release certain chemicals or regulate certain processes.
Histamine H1 receptors are primarily found in smooth muscle, blood vessels, and lymphatic vessels. They are involved with acute responses to pathogens and play a major part in allergic responses to particular substances.
Allergic reactions occur when an individual has a sensitivity to a specific substance, which the immune system recognizes and interprets as a threat to be destroyed or eliminated. The local inflammatory action of histamine is what causes allergic symptoms such as wheezing and constricted breathing, while allergic symptoms such as watery eyes and sneezing are the result of the body attempting to forcibly eject allergens. Antihistamines, which are drugs used to control allergy symptoms, primarily work by preventing histamine from binding with histamine H1 receptors.
Histamine H2 receptors are mainly located in the stomach. The binding of histamine with H2 receptors tells the body to secrete gastric acid, which activates enzymes that facilitate digestion.
Histamine H3 receptors mainly reside in the brain and spinal cord. They work in conjunction with histamine to modulate chemical signals in the central nervous system.
Histamine H4 receptors were discovered in the relatively recent past, and they are most heavily concentrated in white blood cells and bone marrow. They are involved in the regulation of highly specific immune system functions and remain the subject of ongoing research.
Studies have found that antihistamines that target specific histamine receptors have no effect on other histamine receptors. For example, antihistamines that stop histamine from binding with H1 receptors provide relief from allergy symptoms but do not prevent histamine from binding with H2 receptors and, therefore, do not interfere with the production of gastric acid.
In most cases, histamine provides an important and effective level of natural health support, helping the body prevent and control the potentially deadly consequences of infections while working to eliminate environmental irritants. However, the allergic responses histamine causes can be harmful and, in extreme cases, deadly. Thus, it is important for individuals with known allergies to be proactive about avoiding exposure to allergens. Antihistamines can provide effective relief from relatively minor symptoms, but more severe allergic reactions are medical emergencies and require more aggressive interventions.
Histamine naturally occurs in some foods, particularly those that have been fermented or aged. High-histamine foods include alcohol, pickled cabbage, smoked meats, aged cheeses, shellfish, nuts, beans, certain legumes (including peanuts), cocoa and chocolate, vinegar, ready-made meals, and canned foods. Eating these foods can cause allergic reactions in sensitive individuals. The related phenomenon of histamine poisoning is specific to fish, which produces high histamine levels when it is not properly stored. Consuming spoiled fish can lead to a form of histamine poisoning that doctors call scombrotoxin fish poisoning.
Bibliography
Abbas, Abul K., et al. Basic Immunology E-Book: Functions and Disorders of the Immune System. Elsevier Health Sciences, 2015.
"Antihistamines–How They Work." National Health Service, 24 Feb. 2015, www.nhs.uk/Conditions/Antihistamines/Pages/How-does-it-work.aspx. Accessed 27 Mar. 2017.
"Histamine and Histamine Receptors." Colorado State University, 20 Dec. 2008, arbl.cvmbs.colostate.edu/hbooks/pathphys/endocrine/otherendo/histamine.html. Accessed 27 Mar. 2017.
Hough, Lindsay B. "Histamine Actions in the Central Nervous System." National Center for Biotechnology Information,www.ncbi.nlm.nih.gov/books/NBK28245/. Accessed 27 Mar. 2017.
"How Does the Immune System Work?" US National Library of Medicine, 30 Oct. 2013, www.ncbi.nlm.nih.gov/pubmedhealth/PMH0072548/. Accessed 27 Mar. 2017.
Khardori, Nancy, et al. Biomedical Aspects of Histamine: Current Perspectives. Springer Science & Business Media, 2010.
Sompayrac, Lauren M. How the Immune System Works. John Wiley & Sons, 2015.
"What Are Histamines?" WebMD, 2016, www.webmd.com/allergies/what-are-histamines#1. Accessed 27 Mar. 2017.