These people do not have colds or the flu . They are just experiencing their annual bout of hay fever . Cause Hay fever , also called allergic rhinitis , is an allergy to pollen or other airborne substances.
Plants produce pollen in the spring.
The pollens of some plants are very light and dry and carried in the air. These are the pollens that cause hay fever. The most common irritants are pollens of weeds such as ragweed, sagebrush, and redroot pigweed. Many people are also allergic to grasses such as timothy, redtops, and rye. Various common trees also produce airborne pollens, including elms, maples, oaks, and birches.