Drug Action: How Antihistamines Work

Antihistamine drugs are used to prevent or relieve the symptoms of allergic reactions, such as a rash. Allergens, such as grass pollen, can trigger the release of the chemical histamine from body cells. This chemical acts on small blood vessels, glands, and other tissues, causing the symptoms of allergy. The drugs work by blocking the action of histamine.

Before drug

Histamine is released in response to an allergen and attaches to sites on tissue cells known as histamine receptors. This causes an allergic reaction in the tissue.

After drug

The antihistamine drug occupies some of the histamine receptors, thereby preventing histamine from attaching to them. This reduces the severity of allergic symptoms.

From the 2010 revision of the Complete Home Medical Guide © Dorling Kindersley Limited.

The subjects, conditions and treatments covered in this encyclopaedia are for information only and may not be covered by your insurance product should you make a claim.

Back to top