The disease, also known as hay fever, is caused by the patient's allergy to plant pollen, mainly involving the eyes and upper respiratory tract. Most of the disease is transmitted by wind, and pollen is used as allergen. The prevalence of pollinosis is closely related to the law of pollen spreading in the air. Thommen proposed that the epidemic plants that can cause pollinosis should have five conditions: ① they must be wind-borne flowers, belonging to airborne pollen; ② High pollen yield; ③ The pollen is light and easy to float far away. The pollen diameter is about 15 ~ 58 μ g; ④ The plant is widely and abundantly grown locally; ⑤ Pollen must have specific antigenic substances. Therefore, the prevalence of pollinosis has an important relationship with the number of sensitized pollen, and has regional and seasonal characteristics. In most parts of China, there are two peak periods of pollen dispersion in Spring Festival and summer and autumn. Pine, cypress, poplar, willow and birch are the main pollen in spring in the north; Artemisia, Jin grass, Chenopodiaceae and Gramineae are the main summer and autumn pollen. The main spring festival pollen in the south is poplar, willow, sycamore, eucalyptus, palm, etc., and the main summer and autumn pollen is Gramineae, Jin grass, amaranth, Ligustrum lucidum, etc. Ragweed pollen has been found in the air in 12 provinces in China, and has become one of the important sensitizing pollen in some areas such as Qingdao and Shenyang. The onset of pollinosis usually requires three sensitization periods of pollen seasons.
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