Antihistamines counteract histamine released by the immune system during an allergic reaction, preventing symptoms such as itching, watery eyes, and airway constriction. Different people are sensitive to different allergens, and antihistamines can be sold over the counter or prescribed for severe reactions.
An antihistamine is a type of drug used to fight allergic reactions. It comprises a large class of drugs that can treat conditions ranging from mild to life-threatening. Different are used for different types of reactions, but at their core they all do the same thing: They counteract a type of chemical released by the body’s immune system, known as histamine.
An allergic reaction occurs when the body is exposed to a harmless external chemical called an allergen, which triggers a false response from the immune system. Antibodies are released into the blood to fight off the perceived threat. As part of the reaction, a type of blood cell, called mast cells, releases the chemical histamine.
Histamine is a powerful stimulant and generally causes great irritation within the body, which can be much worse than any threat posed by the allergen. The resulting irritation is called an allergic reaction, and depending on the severity of the reaction, it can cause a variety of symptoms that include itching, watery eyes, runny nose, rash, airway constriction, vomiting, and diarrhea. In extreme cases, a condition called anaphylaxis can occur, spreading rapidly throughout the body, with potentially fatal results.
Different people’s immune systems vary widely in terms of the allergens they are sensitive to. As a result, one person may have a severe allergic reaction to a certain type of food, such as fish, while another will have no reaction at all. Pollen is one of the most common allergens among humans, causing seasonal allergies in spring and autumn. Drug allergies are often more severe, sometimes resulting in severe skin rashes. More recently, extreme peanut allergy is on the rise, especially among children. Those with this type of allergy are at risk of experiencing anaphylaxis if they don’t get the needed type of antihistamine quickly enough.
When an antihistamine is given, it prevents the histamine from reaching the receptors on the cells at the site of irritation, thus preventing the allergic reaction. Some classes are designed to block receptors throughout the body. Many of these are sold over the counter and tend to cause drowsiness. For this reason, antihistamines are the main active ingredient in many medicines used to treat insomnia. There are also some newer medications that target specific areas of the body for a more localized effect, without causing drowsiness. Stronger prescription drugs are available for severe reactions.
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