Histamine is a chemical in the body that is released when the body is exposed to an allergen. Allergens may include airborne allergens (such as pollen and dust mites), certain foods (such as peanuts and shellfish) or insect venom. Histamine is released in an effort to protect the body from an allergen; however, sometimes an overload of histamine can result in life-threatening symptoms.
Smooth Muscle Contractions
The release of histamine can cause smooth muscles around the lungs or intestinal tract to contract. Such contractions can make breathing difficult or can cause gastrointestinal distress.
Nervous System Response
Excess histamine can lead to nervous system reactions such as drowsiness and confusion.
Histamine can also cause inflammation that results in hives or inflamed airways.
When an allergen is inhaled, histamine causes the blood vessels to become dilated, which in turn causes fluids to leak out of the facial tissues, resulting in watery eyes, runny nose, stuffy nose, sneezing and itching.
Individuals can be extremely allergic to certain substances such as pollen, insect venom, latex, food items and some medications. These individuals may suffer from anaphylaxis, a life-threatening condition, when excess amounts of histamine are released into the body. Symptoms of anaphylaxis include hives, itching, pale or flushed skin, dizziness, fainting, airway constriction, swollen throat, swollen tongue, rapid or weak pulse and stomach symptoms such as nausea, diarrhea or vomiting.