A new study published in Scientific Reports investigated the levels of exposure to Japanese cedar pollen that could increase the risk of sensitization and allergic reaction. This was a cross-sectional study that enrolled 857 college students living in Jeju, South Korea. These students underwent questionnaires about demographic characteristics and skin prick tests for allergic sensitization. The results revealed that the sensitization rates of groups divided by residence period were 3.8% in less than 1 year; 1.8% in 1-2 years; 8.5% in 2-3 years; 10.3% in 3-4 years; 14.8% in 4-10 years; and 19.1% over 10 years. Residence period was an influencing factor of sensitization rate to Japanese cedar pollen and the cut-off value of the residence period that increased the risk of sensitization to this allergen was found to be 25 months. While repeated exposure to seasonal allergens was related to an increased sensitization rate in young adults. From the findings, it was concluded that exposure to Japanese cedar pollen for over two seasons could increase the risk of an allergic reaction in adults.