Pollen reactivity in respiratory allergic diseases has recently increased in Korea. According to changes in allergen sensitization over the last 30 years, tree pollen sensitization in the 2010s markedly increased in oak, birch, alder, and pine. The sensitization to grasses and most weeds in the 2010s decreased in comparison with the 90s results. Oak Pollen allergens have increased in air during the last 30 years, and this increment has been correlated with increased oak reactivity. The number of birch trees is not so many as oak, but skin reactivity to birch pollen is as same as that to oak pollen. Because there are many chestnut near the residence, sensitization to Castanea spp. has to be evaluated. Maidenhair tree and Japanese elm are regarded as offending allergens of pollenosis. There are many maindenhair trees (Ginkgo biloba) and Japanese elm (Zelkova serrata) on streets and in park areas, and they produce a large amount of anemophilous pollen in spring. There is little wide grassland in Korea except the rice fields. Therefore, we do not have dominant grasses for pollenosis. There are a few peculiar grasses, such as orange foxtail, common reed, Korean lawn grass, Chinese silver grass, and green bristle grass. These pollens should be evaluated for cross-allergenicity with known allergenic pollens, such as timothy and Bermuda grass. In Korea, sagebrush, ragweed, and hop Japanese are prominent plants in autumn. Chrysanthemum spp. should be further evaluated because of persistently increased sensitization during the last 30 years, which are widely distributed in wild fields and bloom massively during late autumn. Recent climate changes and air pollution increase pollen production and alter pollen allergenicity. Therefore, continuous monitoring of plant ecology and pollen sensitization is necessary in effectively controlling pollen allergy for human health.