immune disorders
Seasonal Allergies
Introduction
Seasonal allergies result from exposure to airborne substances (such as pollens) that appear only during certain times of the year. Seasonal allergies cause itchy skin, a runny nose, sneezing, and sometimes itchy or watery, bloodshot eyes. Doctors can usually diagnose these allergies when typical symptoms (such as a runny, itchy nose and itchy eyes) develop during a particular season. Corticosteroid nasal sprays, antihistamines, and decongestants help relieve symptoms. (See also Overview of Allergic Reactions .) Seasonal allergies (commonly called hay fever) are common. They occur only during certain times of the year—particularly the spring, summer, or fall—depending on what a person is allergic to. Symptoms involve primarily the membrane lining the nose, causing Allergic Rhinitis , or the membrane lining the eyelids and covering the whites of the eyes (conjunctiva), causing The term hay fever is somewhat misleading because symptoms do not occur only in the summer when hay is traditionally gathered and never include fever. Hay fever is usually a reaction to pollens and grasses. The pollens that cause hay fever vary by season: Spring:Usually trees (such as oak, elm, alder, birch, beech, poplar, ash, and olive) Summer:Grasses (such as Bermuda, timothy, sweet vernal, orchard, and Johnson grass) and weeds (such as Russian thistle and English plantain) Fall:Ragweed Also, different parts of the country have very different pollen seasons. In the western United States, mountain cedar (a juniper) is one of the main sources of tree pollen from December to March. In the arid Southwest, grasses pollinate for much longer, and in the fall, pollen from weeds, such as sagebrush and Russian thistle, can cause hay fever. People may react to one or more pollens, so their pollen allergy season may be from early spring to late fall. Seasonal allergy is also caused by mold spores, which can be airborne for long periods of time during the spring, summer, and fall. Allergic conjunctivitis may result when airborne substances, such as pollens, contact the eyes directly. 