Hay fever, also known as seasonal allergic rhinitis, is an allergy-related inflammation of the nasal passages, throat and eye membrane (conjunctiva), caused by sensitivity to airborne pollens and molds. These airborne pollens come from various species of trees, grasses, weeds and other plants whose pollens are carried by the wind rather than by insects. Because different types of pollen trigger symptoms in different people, each person's specific hay fever "season" is fairly predictable and is related to times when their allergy-triggering plant is in bloom. For example, for people who are allergic to tree pollens and who live in temperate North America, symptoms usually are worst from March through May, when trees are blossoming. June and July are peak months for people allergic to grasses, while people with ragweed allergies suffer the worst symptoms from mid-August through October. Since molds depend on damp, dark conditions, people who are allergic to molds tend to have the least predictable allergy season. They usually find that their symptoms are more related to warm, rainy weather. In the United States, this means summer and fall are peak times.
Hay fever and its sister ailment, perennial allergic rhinitis (a year-round sensitivity to animal dander, dust mites or cockroaches), are most common in people who have a family history of allergies or a personal history of allergy-related conditions, such as eczema and childhood asthma. Currently, about 20% of people in the United States suffer from either seasonal or perennial allergic rhinitis. Although seasonal allergic rhinitis can affect people in all age groups, its symptoms generally peak during childhood and adolescence.