Hay fever is an allergic reaction that makes your nose run, your eyes itch and water, and causes sneezing fits, usually triggered by pollen from trees, grass, or weeds floating through the air. Despite its name, hay fever has nothing to do with hay and doesn't cause a fever. It's called that because it often strikes during haying season in late summer, when farmers traditionally cut and dry grass for animal feed.

When you have hay fever, your body's immune system mistakenly treats harmless pollen as a dangerous invader, like a virus or bacteria. It launches an aggressive defense that causes all those uncomfortable symptoms. Some people get hay fever in spring when trees release pollen, others in summer when grass pollinates, and some in fall when ragweed spreads its pollen on the wind.

Doctors call hay fever allergic rhinitis. About one in five people experience it. While hay fever can make you miserable during pollen season, it's not contagious and usually responds well to antihistamine medicines. Many people with hay fever learn to check pollen counts before planning outdoor activities, the same way others check the weather forecast before a picnic.