(1) Obvious seasonality: in the north, for example, tree pollen mostly develops in spring, grass pollen mostly develops in summer, and weed pollen mostly develops in autumn. (2) distinct regional: the symptoms of hay fever patients in the north disappear or are significantly relieved after going to the south during the onset period, and similarly, hay fever patients in the south will be greatly relieved or even disappear after going to the north during the onset period.