One in two people are reported to suffer from hay fever, which is now called a "national disease." With this in mind, a research group from Nagoya University and others reported that tin in "PM2.5," air pollutant fine particulate matter, may worsen the symptoms of allergic rhinitis such as cedar pollinosis. The tin concentration in the nose of hay fever sufferers is about 3 to 4 times higher than that of people without symptoms. This retention of tin in the nasal cavity may be related to worsening symptoms.
According to a research group led by Professor Masashi Kato and Lecturer Akira Tazaki of the Graduate School of Medicine at Nagoya University, with participation from the University of Fukui and Nagoya City University, tin is contained in particulate matter with a diameter of 2.5 micrometers or less (PM2.5). Kato and his colleagues have previously reported that lead, another air pollutant, worsens symptoms of allergic rhinitis. This time, to clarify the relationship with tin, the research group examined tin concentrations in the nasal rinses from 44 people who had symptoms and 57 people who had no symptoms during the cedar pollen dispersal period.
The results showed that the tin concentrations in those with symptoms were 3 to 4 times higher than those without symptoms. The research group next conducted an experiment using a mouse model of allergic rhinitis. When tin was put into the nasal cavity of mice at a level comparable to that in the nasal cavity of hay fever sufferers, the allergic symptoms worsened in the mice.
Provided by MOE and MHLW
Model mice were given PM2.5-like aerosols containing tin at a level equivalent to the actual dispersion environment. The results showed that tin accumulated in the nasal cavity of the rhinitis model mice was 2 to 3 times higher than that in the nasal cavity of the normal mice. This indicates that PM2.5 is trapped in the nasal cavity and accumulates more in allergic rhinitis.
The research group also proceeded with a study combining chemical analysis of mouse pathological tissues with an analytical technique called "elemental imaging." They found that the model mice with rhinitis symptoms had increased levels of mucin, a mucus component in the nasal cavity, with tin and mucin co-localized at a frequency as high as 67%. They also found that mucin production was increased upon exposure to tin.
It has been pointed out that air pollutants may worsen cedar pollinosis, but the detailed mechanism has not been elucidated. According to Kato and his colleagues, when individuals with symptoms of cedar pollen allergic rhinitis are exposed to PM2.5-derived tin, allergic reaction increases mucin, which traps and retains tin in the nasal cavity for a long time. Retained tin further worsens the symptoms. The mechanism of this vicious cycle was revealed.
The research results were published online in the international journal Allergology on December 2, 2025.
Provided by Nagoya University
According to the MOE and MHLW, repeated pollen exposure over several years to several decades, although considerably different among individuals, leads to increased levels of antibodies that recognize pollen as a foreign substance (antigen) in the body. This causes hay fever symptoms such as sneezing, runny nose, and itchy eyes. Treatment for severe symptoms includes symptomatic treatment with oral medication and nasal and/or eye drops, as well as a method called allergen immunotherapy, in which tablets containing cedar pollen components are administered on a regular basis.
Large amounts of cedar pollen disperse in February through April. According to an MOE announcement in December 2025, the amount of cedar pollen dispersed each spring can be predicted by the amount of cedar cones produced in the previous autumn. The flowering amount refers to the amount of pollen cones that cedar trees produce in a year. According to a survey in the autumn of 2025, the flowering levels were more than twice the average of the past 10 years in 9 prefectures, i.e., Hokkaido, Yamagata, Shizuoka, Aichi, Kyoto, Osaka, Nara, Tottori, and Tokushima.
The government has designated "measures for onset prevention," "measures for source reduction," and "measures for dispersal prevention" as the three pillars of hay fever countermeasures. Of these, the government promotes measures to reduce cedar plantation areas by approximately 20% by FY2033 as the measures for source reduction.
Original article was provided by the Science Portal and has been translated by Science Japan.