Allergy-causing substances like pollen and dander may cause dilatation of blood vessels in the conjunctiva, the membrane covering the eye. The resulting reddening of the eyes is called allergic conjunctivitis, and is usually accompanied by itching and tearing.
Review Date 8/13/2020
Updated by: Linda J. Vorvick, MD, Clinical Associate Professor, Department of Family Medicine, UW Medicine, School of Medicine, University of Washington, Seattle, WA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.