According to Wikipedia [0], Hayfever was already described in the 10th century. It is less common among people who grew up on a farm and more common with rising temperatures and air pollution. Hayfever is also significantly more common in urban areas.
Assumably all of these factors play a role in the prevalence today, though that doesn't rule out the existence of other undiscovered factors (e.g. a disease, as some people speculated).
Assumably all of these factors play a role in the prevalence today, though that doesn't rule out the existence of other undiscovered factors (e.g. a disease, as some people speculated).
[0] https://en.wikipedia.org/wiki/Allergic_rhinitis#History