Histamine Reaction

Histamine is an organic nitrogen compound that is derived from the decarboxylation of the amino acid, histidine. This chemical is associated with allergies or allergic reactions. An allergic reaction refers to the hypersensitivity reaction of the immune system to certain potentially harmless substances like dust, pollen, mites, etc. A hypersensitive immune system recognizes such harmless substances as foreign invaders, and then stimulates the production of antibodies to destroy them. This in turn induces the release of chemicals like histamine, which is responsible for triggering the inflammatory response of the body. Any substance that can stimulate allergic reactions is known as an allergen. Histamine is the main chemical that is associated with many allergic reactions. Causes and symptoms of histamine reaction, along with the treatment, are described in the paragraphs below.

What is a Histamine Reaction?
Histamine is released by the mast cells and basophils during an allergic reaction. Histamine can affect various parts of the body. There are several histamine receptors in our body. A histamine reaction is produced as a result of the effect of histamine on a particular histamine receptor. In general, histamine can trigger the inflammatory response of the body by dilating the blood vessels. As a result, the permeability of the blood vessels increases, which in turn allows more fluid to enter the skin and cause swelling. Dilation of blood vessels can also cause redness.

The blood vessels are dilated during an allergic reaction so that the white blood cells can get access to the foreign invaders. Apart from dilating the blood vessels, histamine can cause the contraction of the smooth muscles, which is responsible for producing asthma attacks. Anaphylaxis is another type of histamine reaction. It is a serious condition that causes severe breathing difficulty along with a significant drop in blood pressure. Some histamine receptors, known as H2 histamine receptors are also present in the cells of the gastric mucosa. When histamine stimulate these receptors, production of gastric acid increases, which causes irritation of the lining of the digestive tract.

Causes
This reaction can be triggered by a large number of allergens. More commonly, this immune response can be triggered by allergens like dust, pollen, animal dander, mold, and mites. Even certain types of foods can stimulate this type of reaction. Many times, insect bites or stings, especially from bees, wasps, fire ants, and hornets can produce histamine or allergic reaction.

Symptoms
A histamine reaction can produce several symptoms by triggering the H1 and H2 receptors. When it stimulates the H1 receptors, one can expect symptoms like, skin rash, hives, swelling, itching along with headaches and respiratory responses. When histamine triggers the H2 receptors, it results in gastric histamine reaction, which is characterized by an excess production of gastric acid. As has been mentioned already, histamine can affect several parts of the body. Mild histamine reaction is characterized allergy symptoms like skin sensitivity, skin rash, itching and hives, swelling, itchy and watery eyes, runny nose and swelling in the sinus cavity, leading to nasal congestion.

When histamine causes the contraction of the smooth muscles, one can experience breathing difficulty or shortness of breath due to obstruction of the airways. These are the classic symptoms of asthma. In severe cases, this reaction can lead to a life-threatening condition, known as anaphylaxis. Anaphylaxis is a systemic reaction, where the airways constrict or swell excessively, which can cause severe shortness of breath and wheezing. Other symptoms of anaphylactic reaction include headache, gastrointestinal problems like diarrhea and vomiting, along with dizziness, confusion and a sudden drop in blood pressure.

Treatment
Histamine reaction is treated with the help of antihistamine drugs. These drugs neutralize the effects of histamines on the body by blocking the histamine receptors. Antihistamines inhibit the action of histamines by blocking the messages sent by them to the histamine receptors. There are two types of antihistamines, H1 antagonists and H2 antagonists. Some common H1 antagonists are diphenhydramine, loratadine, and cetirizine. The term antihistamines is more commonly used to refer to H1 antihistamines, which are used for treating the symptoms of local inflammation and runny nose or nasal congestion. Examples of H2 antagonists are cimetidine, roxatidine, famotidine, ranitidine and nizatidine. These are mainly used for reducing the production of gastric acid, and for treating conditions like gastroesophageal reflux disease and peptic ulcers.

Histamine reaction usually produces mild to moderate symptoms, which can be easily alleviated with antihistamine medications. However, release of a large amount of histamine in the body can cause some serious problems like breathing difficulty. Therefore, the symptoms of histamine or allergic reaction should not be neglected. These symptoms should be immediately reported to a physician to ensure prompt treatment of the condition.