TreatAllergies.com

Antihistamines work to reduce allergy symptoms by blocking the release of a natural chemical known as histamine. When you have an allergy, you body mistakenly releases histamine in response to a benign foreign substance, an allergen, that it mistakes for a threatening antigen. Typically, histamine produces sneezing, itchy eyes, a runny nose and rashes (usually hives). By reducing the amount of histamine in the body, antihistamines can alleviate these symptoms but they cannot treat the cause of the allergy.