When there is an allergic reaction in the body, a chemical called histamine, from specialized cells in the body tissues is released. Histamine causes allergy symptoms such as sneezing, itching, watery eyes, and runny nose. Antihistamines may reduce inflammation, itching, and swelling by blocking the effects of histamine, reducing the allergy symptoms.
Review Date 4/14/2015
Updated by: Kevin Berman, MD, PhD, Atlanta Center for Dermatologic Disease, Atlanta, GA. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Isla Ogilvie, PhD, and the A.D.A.M. Editorial team.