Background The most ordinary trees, grasses, and weeds manufacture pollen, often in extraordinary amounts. These tiny, light, and dry particles are built for wind transport and can remain airborne for hundreds of miles. Although spring and fall are the primary seasons for hay fever (seasonal allergic rhinitis), those who live in milder climates may experience allergies year-round. Because variations in temperature and rain-fall affect how much pollen is in the air, some seasons and years will be worse than others.
Incidence and Prevalence An estimated 15-20% of the United States population, 44 to 58 million Americans, experiences some degree of hay fever. The condition is found in equal percentages among men and women and can be triggered by inhaling or touching pollen.
Cause and Risk Factors Pollen can get into the airways (mouth, nose, throat, and lungs) through breathing or linings of the eyes. Once into the body, the pollen particles interact with the immune system, triggering hay fever symptoms. The most common of these symptoms are itchy, puffy, and watery eyes, sneezing, and a running nose or nasal congestion. In more severe cases, airborne allergens can cause reduced lung capacity and difficulty breathing. Contact allergies can manifest in hives or skin rashes.
Risk factors for hay fever include family members, especially parents, with allergies, frequent exposure to pollens, other allergic conditions such as eczema or asthma, and nasal polyps (small, non-cancerous growths in the lining of the nose).