Histamine H1 receptor antagonists comprise the largest class of medications used in the treatment of allergic disorders, especially asthma, rhinitis and urticaria. They are administered for their ability to produce blockade of histamine action at H1 receptors. Age, race, gender, body-weight, hepatic and renal function influenced the pharmacokinetics of H1 antagonist. During the last years, the second generation of histamine H1 receptor antagonists has been developed to reduce or eliminate the sedation and the anticholinergic adverse effects that occur with older antihistamines. Several synthetized antihistamine drugs have been studied in allergic rhinitis, asthma, urticaria and dermatitis. All second-generation H1 antagonists offer a superior clinical profile compared with the older antihistamines. All the new drugs have good clinical efficacy. The overall pathogenic view of respiratory allergy has profoundly changed and evolved over the past ten years. Particular attention has been paid to the relationship between rhinitis and asthma and between the upper and lower respiratory airways. According to the operative definition of allergic rhinobronchitis or, as recently proposed, of united airways disease (UAD). The increase in knowledge of the mechanisms of allergic inflammation in the respiratory tract has partly clarified the pathophysiology of allergic and non-allergic diseases that can involve nose, bronchi and skin. The concept of UAD has also relevant diagnostic and therapeutic implications. The more recent antihistamine medications may have an important role in controlling the inflammation induced by allergic stimuli affecting all airways.