Apart from wide-spectrum antibiotics, antihistamines are possibly the most widely prescribed systemic drugs in dermatologic practice. Use of antihistamines in urticaria is universal because histamine is an important mediator of symptoms in most types of urticaria. In atopic eczema, their importance is more controversial, some authors asserting that their value depends on central sedative rather than peripheral antihistamine activity. Most patients with atopic eczema receive antihistamines at some stage in their management. Other diseases in which antihistamines may be useful include mastocytosis and insect bite reactions.