The term 'histamine' refers to an organic nitrogen compound that is derived from the decarboxylation of the amino acid, histidine. 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.
An allergic reaction refers to the hypersensitivity reaction of the immune system to certain potentially harmless substances that are referred to as allergens. Some of the common allergens are:
- Animal dander
- Insect bites
- Stings, especially from bees, wasps, fire ants, and hornets
- Dairy Products
- Tree nuts
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. The blood vessels are dilated during an allergic reaction so that the white blood cells can get access to the foreign invaders. This 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.
- 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.
- Mild reaction is characterized by 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 asanaphylaxis. 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.
A 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.
H1 antagonists: 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. Some common H1 antagonists are diphenhydramine, loratadine, and cetirizine
H2 antagonists: These are mainly used for reducing the production of gastric acid, and for treating conditions like gastroesophageal reflux disease and peptic ulcers. Some common H2 antagonists are cimetidine, roxatidine, famotidine, ranitidine and nizatidine.
An allergic reaction that produces mild to moderate symptoms can be easily treated with antihistamine medications. However, release of a large amount of histamine in the body can cause anaphylaxis, which requires immediate medical assistance owing to its life-threatening nature. 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.
Disclaimer: The information provided in this article is solely for educating the reader. It is not intended to be a substitute for the advice of a medical expert.