A reforestation decision made more than 70 years ago in Japão, shortly after Segunda Guerra Mundial, turned into a national public health crisis. The country is facing an epidemic of seasonal allergies caused by the massive planting of just two species of native trees: the Japanese cedar (sugi) and the Japanese cypress (hinoki).
Aproximadamente 43% of the Japanese population suffers from moderate to severe symptoms of hay fever in spring. The rate exceeds that of other countries by a large margin — in Reino Unido it is 26% and in Estados Unidos it varies between 12% and 18%. Videos released in February 2026, showing what appeared to be smoke rising from conifer plantations, revealed the truth: dense clouds of pollen invading entire cities.
Origem of Crisis: Post-War Decision
Durante to Segunda Guerra Mundial, the scarcity of natural oil and gas forced Japão to heavily exploit its forests as a source of fuel. Widespread deforestation has left the mountains near towns like Tóquio, Osaka, and Kobe completely devoid of vegetation cover. Montanhas naked increased risks of landslides and floods.
Para To quickly reverse the scenario, the government implemented a large-scale reforestation program in the decades following the war. The strategy focused on two fast-growing native species: sugi and hinoki. The trees would provide future timber for construction while protecting the soil from erosion. Conforme explains Noriko Sato, professor and forestry researcher at Universidade of Kyushu, the initiative was financed with public resources through government works.
The choice prioritized speed over diversity. The two species develop quickly in temporary climates and would consolidate forest recovery in decades — not centuries.
Current Escala and pollen production
Hoje, hinoki and sugi plantations cover approximately 10 million hectares — one-fifth of Japan’s entire land area. Essas monoculture forests reached maturity years ago. The problem has intensified because trees release increasing amounts of pollen after they are 30 years old, a stage that practically all forest cover has already surpassed.
Every spring, particularly as the seasons come earlier due to climate change, enormous amounts of light pollen simultaneously fall off crops and are carried by the wind toward cities. Sugi and hinoki pollen, unlike other species, disperses easily in the atmosphere, reaching large urban territories and causing inflammation of the nasal passages.
Impacto in public health
The effects go beyond seasonal discomfort. Affected Pessoas develop insomnia and difficulty concentrating during critical months. Portadores pollen allergy sufferers are highly likely to develop related conditions such as asthma and food allergies.
The economic cost is substantial:
- Impacto daily financial estimated at US$ 1.6 billion (approximately R$ 8.5 billion) at the height of the season
- Perda associated with sick leave
- Queda in consumption during peaks of allergic crisis
- Demanda rising for medicines and surgical masks
- Redução of productivity in affected cities
Durante Spring, scenes repeat themselves on the streets of Japanese cities: citizens of all ages wearing surgical masks, many carrying medicines. Hay fever — also known as allergic rhinitis — has become a national health emergency.
Busca by solutions
Pesquisadores and Noriko Sato indicate urgency in resolving the problem. Embora Several proposals circulate among experts — including gradual replacement of pollen-producing trees with alternative species and differentiated forest management — no quick solution exists to reverse 70 years of monoculture plantations.
The crisis illustrates the paradox of long-term public policies: decisions aimed at solving immediate problems in the past can generate unforeseen consequences in the future. Japão now seeks to balance the preservation of its forests with the urgent need to mitigate a public health epidemic affecting tens of millions of inhabitants.