Mast cells release histamine when an allergen is encountered. The histamine response can produce sneezing, itching, hives and watery eyes.
Stuart I. Henochowicz, MD, FACP, Associate Clinical Professor of Medicine, Division of Allergy, Immunology, and Rheumatology, Georgetown University Medical School. David Zieve, MD, MHA, Medical Director, A.D.A.M. Health Solutions, Ebix, Inc.