Why is hay fever called hay fever?

Hay fever is called so because it was originally thought to be triggered by hay and the pollen from grass and other plants during the hay-making season. The term "fever" refers to the allergic reaction that can cause symptoms like sneezing, nasal congestion, and itchy eyes, resembling a mild fever, even though it doesn’t involve an actual fever. Today, we understand that hay fever, or allergic rhinitis, can be triggered by various allergens, including pollen, dust, and pet dander, not just hay.