In these conditions they work by preventing the actions of histamine, which is a substance produced by the body as part of its natural defences.It's stored in cells called mast cells, in almost all tissues of the body, and is released when the body reacts to a foreign substance (known as an allergen).Antihistamines are medicines that can be used to relieve severe itching and help break this cycle.Often you will find that the itchiness of your skin is reduced when you use regular moisturisers to keep the skin soothed and hydrated, and control the inflammation with topical corticosteroids or other newer medicines.
However, if itching is still a problem your doctor may prescribe you an antihistamine.
Antihistamines are most commonly used to control the symptoms of allergies such as hay fever.
The released histamine binds to its receptors (H-1 receptors) causing a chain reaction that includes an increase in blood flow to the area, and the release of other chemicals that add to the allergic response. Antihistamines work by blocking histamine receptors, therefore reducing the reactions that cause itching.
However, histamine is only one of many substances in the body that cause itching, and these medicines are mainly of value because they cause sedation.
This is often referred to as an 'itch-scratch-itch' cycle.
It leads to thickening and weeping of the skin and generally makes the eczema worse and more likely to become infected because scratching breaks the skin.