Histamine release is a biological response mediated by the immune system in response to allergens and certain other triggers from the outside environment or the body itself. In this response, basophils and mast cells respond to a protein, such as an immunoglobulin attached to an allergen, by releasing histamine, a chemical compound produced and stored in these cells. A cascading series of reactions occurs as the histamine connects to receptors in neighboring tissues.
When histamine release occurs, several things happen. The compound forces blood vessels to dilate, lowering blood pressure and increasing the flow of blood to the area. Blood vessel walls also become more permeable, allowing compounds rushing to the site to pass into the surrounding tissue. This usually causes swelling and flushing. The tissue may itch, tingle, or hurt, depending on the intensity of the response.
In the airways, histamine release can be dangerous, as this compound also forces smooth muscle contractions. The airway is made of smooth muscle and it may contract as well as swelling, limiting the supply of air to the lungs. Histamine release is associated with asthma attacks, as well as closure of the airways in cases of severe allergies, where being exposed to an allergen causes a widespread histamine release and accompanying severe symptoms.
Histamine is also active in the central nervous system, including in the brain, where it can inhibit or interrupt neurotransmitters and acts as a neurotransmitter itself. Histamine plays a role in sleep and the mediation of physical responses to stress and may perform other functions in the brain as well.
In allergic reactions, the immune system experiences a disproportionate response to an allergen. This includes histamine release, with too much histamine being released at a given site, leading to severe inflammation. The intensity of the response triggers corresponding intensity in the linked steps of the immune response. This can potentially be fatal for the patient as the immune system essentially loses control and fails to moderate the immune response to make it more proportionate to the allergen involved.
Medications known as antihistamines can block or limit histamine release to decrease the intensity of immune reactions. These medications can be used in the management of asthma and allergies to protect patients from debilitating or dangerous immune reactions. Many are available over the counter for treatment of issues like season allergies leading to allergic rhinitis and eye irritation. Others are offered by prescription only.