How do antihistamines work?

Antihistamines -- available as tablets, nasal sprays, and eye drops -- help relieve allergy symptoms by blocking the effects of histamine, a substance released by your body when you're exposed to an irritant. Antihistamines help reduce itching, sneezing, runny nose, and itchy, watery eyes. For congestion relief, antihistamine nasal sprays are more effective than tablets.

Second-generation antihistamines (such as loratadine and fexofenadine) are recommended over first-generation for treating seasonal allergies. These newer drugs have fewer side effects and are low-sedating or nonsedating, so they don't cause as much drowsiness as their older counterparts.