Histamine and antihistamines in atopic dermatitis

Itching (pruritus) is perhaps the most common symptom associated with inflammatory skin diseases and can be a lead symptom ofextracutaneous disease (e.g., malignancy, infection, metabolic disorders). In atopic dermatitis itching sensations constitute one of the most prominent and distressing features. The most characteristic response to itching is the scratch reflex: a more or less voluntary, often sub-conscious motor activity, to counteract the itch by slightly painful stimuli. The benefit of a short-termed relieve from itching through this scratch reflex though is counteracted by a simultaneous damage of the epidermal layer of the skin which leads to increased transepidermal water loss and drying, which in turn results in a cycle of more itching and more scratching. A wide range of peripheral itch-inducing stimuli generated within or administered to the skin are able to trigger pruritus, one of them being histamine. Based on early experiments, histamine has been suggested to may play a key role in the pathogenesis ofAD. This is reflected by a history for antihistamines in the therapeutic medication of AD patients. Antihistamines are believed to share a common antipruritic effect and therefore are prescribed to the vast majority of AD patient suffering from itch to act alleviating. The level of evidence in support of the benefits of antihistamine treatment, however, is low. To assess the benefit of antihistamines in the treatment of AD in a better way, their mechanisms and specific effects need to be understood more precisely. In particular their precise indication is crucial for successful use. This book chapter will therefore summarize and assess the role of histamine in AD and the efficacy of antihistamines in its treatment based on results of basic research and clinical studies.