Antihistamines

Antihistamines

Histamine Role in Allergic Reactions

Histamine is a chemical that the body naturally releases as part of its defence system. It is deposited in mast cells, which are present in almost all tissues. When the body encounters a foreign substance called an allergen (such as flower pollen), these mast cells release histamine.

Once released, histamine binds to H1 receptors, initiating a series of reactions that lead to allergic symptoms. These include increased blood movement to the affected area and the release of additional chemicals that intensify the allergic response. This process contributes to the symptoms of allergies. For example, histamine in hay fever causes nasal and eye inflammation, resulting in watery, itchy eyes, sneezing, nasal congestion and a runny nose.

How Does Antihistamines Work?

Antihistamines are medications that help ease allergy symptoms by blocking H1 receptors. While they do not stop the mast cells from releasing histamine, they prevent histamine from attaching to its receptors. In turn, this inhibits the release of new allergy-inducing chemicals and reduces blood flow to the region, easing symptoms like those of hay fever.

Antihistamines are also used to treat allergic skin conditions such as urticaria, also known as hives or nettle rash. These conditions cause an itchy rash; and by blocking the effects of histamine, antihistamines help reduce itching and minimize the rash.

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