Second-generation antihistamines are a class of drugs that include Loratadine, Desloratadine, Fexofenadine, and Cetirizine. These drugs work by blocking H1 histamine receptors, thereby reducing histamine-mediated vasodilation and vascular permeability. By inhibiting the effects of histamine, these drugs can be used to treat allergy symptoms, like nasal mucus production and watery eyes. Importantly, second generation antihistamines do not have as many side effects as first generation antihistamines, since they are more selective for H1 receptors and cannot pass through the blood brain barrier to work at central histamine receptors. As such, they do not cause sedation and also do not have the anticholinergic or alpha-blocking effects characteristic of the first-generation antihistamine drugs.