Histamine reactions are a defense mechanism employed by the immune system to protect the body from allergens. When the immune system comes in contact with an allergen, it sends out the chemical histamine. Histamine reactions may include nasal swelling, rashes, and itchy eyes. Severity of a histamine reaction can range from mild to severe. Severe allergic reactions may require medical attention.
When a foreign substance or allergen enters the body, the immune system triggers production of immunoglobulin E, also known as IgE antibody. The antibody pairs up with white blood cells in the bloodstream and rushes to the foreign substance. For instance, if an allergen is inhaled through the nose, IgE and white blood cells will rush to the nose.
When IgE and white blood cells reach the allergen, mast cells are alerted to produce histamine. Histamine causes allergy symptoms such as sneezing, watery eyes, and skin rashes. When too much histamine is released or if the body is sensitive to histamine, a severe allergic reaction could occur.
The effects of severe histamine reactions may include shortness of breath, labored breathing, or swelling. In a small number of cases, severe histamine reactions may lead to anaphylaxis, or anaphylactic shock. Anaphylactic shock is a combination of histamine reactions and lung restriction. Blood pressure drops and breathing is impaired or may become impossible.
Anaphylactic shock can be life-threatening if medical treatment is not administered within a short time. Treatment for a severe histamine reaction such as anaphylactic shock may include self-administered epinephrine shots. Epinephrine shots require a medical prescription. Not all histamine reactions will require medical attention — in many cases, over-the-counter medications or avoidance may be enough to treat mild symptoms.
A histamine reaction can be triggered by environmental substances, animals, and foods. Common environmental allergens include dust, pollen, and mold. Three animals that commonly cause allergic reactions include dogs, cats, and horses. Adults and children also may suffer from food allergies that cause histamine reactions. Peanuts, milk, and strawberries are of particular concern in children.
Symptoms of histamine reactions may be seasonal or situational. Seasonal allergies include pollen and ragweed. Situational allergies may include animal or food allergies. If the histamine reaction to seasonal or situational allergies are severe, doctors may suggest avoidance along with prescribing emergency medications, such as an epinephrine shot. If a shot is used, the patient must immediately be taken to a hospital emergency room for medical attention.