A class of drugs called antihistamines is frequently prescribed to treat allergies and allergic responses. They function by preventing histamine, a substance that immune cells release in reaction to allergens, from doing its job. Itching, sneezing, runny nose, watery eyes, and swelling are some of the signs of allergic reactions that are brought on by histamine. Antihistamines work in the following ways:

Histamine Receptor Blockade: Antihistamines function by attaching themselves to target cells’ histamine receptors, blocking the action of histamine by binding to and activating these receptors. There are various subtypes of histamine receptors, such as H1, H2, H3, and H4 receptors. The primary function of H1 receptors is to mediate allergic responses. The primary target of antihistamines used to treat allergies is the H1 receptor.

Histamine Effects Inhibition: Antihistamines work by preventing histamine from binding to its receptors.

Vasodilation and Vascular Permeability: Histamine causes tissue swelling and inflammation by binding to H1 receptors on blood vessel endothelial cells, which widens blood vessels and raises vascular permeability. By inhibiting histamine-mediated vasodilation and decreasing vascular permeability, antihistamines reverse these effects and relieve symptoms like runny nose, hives, and nasal congestion.

Reduced Itching and Skin Rash: One of the main mediators of allergic reactions’ itching and skin irritation is histamine. Antihistamines lessen itching and aid in the relief of skin rash, hives, and other allergic dermatological symptoms by inhibiting histamine receptors in the skin.

Effects on the Central Nervous System: Because some antihistamines can pass across the blood-brain barrier, they have extra effects on the central nervous system (CNS), especially first-generation antihistamines