Most allergy medicines work by blocking a chemical produced by the body called histamine, which is what causes allergy symptoms. The more popular brands (generic names in brackets) of antihistamines are

• Allegra (fexofenadine)
• Benadryl (diphenhydramine)
• Chlor-Trimeton (chlorpheniramine)
• Clarinex (desloratadine)
• Claritin (loratadine)
• Dimetapp (brompheniramine)
• Zyrtec (cetirizine)

Some of these, like Allegra, Claritin, and Zyrtec have the "D" variety, where D stands for decongestant. In addition to the antihistamine content, they also have pseudoephedrine, to help relieve swelling and stuffy nose.

Another allergy medicine is Singulair. Instead of blocking histamines, it tackles another set of chemicals called leukotrienes, also produced during episodes of inflammation or swelling.

Now, the manufacturers of Claritin and Singulair are seeking FDA approval for a new drug which would combine the active ingredient in Singulair (montelukast) with the active ingredient in Claritin product (loratadine). This combo should be able to treat both types of allergic rhinitis: seasonal allergies i.e., pollen allergies, as well as the perennial allergic rhinitis (mold, dust, dander, etc).