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Japan is facing a nationwide allergy problem rooted in a decision made more than 70 years ago, when large areas of the country were replanted with only two fast-growing tree species after World War II.
Every spring, streets across Japan fill up with people wearing masks as dense pollen triggers hay fever, a seasonal allergy that can cause sneezing, congestion, irritated eyes and serious discomfort. In February, videos showing clouds rising from forests went viral across the country.
Although the images looked like smoke, they showed pollen being released into the air, reminding millions to prepare masks and allergy medicine.
Hay fever has grown into a national crisis in Japan, where an estimated 43% of the population experiences moderate to severe symptoms.
That rate is far higher than in Britain, where the figure is about 26%, and the United States, where it is estimated at around 12% to 18%. Beyond daily discomfort, the allergies can lead to sleep loss, lack of concentration and a higher risk of related conditions such as asthma or food allergies.
The impact also reaches into the economy. During the peak of Japan’s hay fever season, losses linked to sick leave and weaker consumer spending are estimated at $1.6 billion a day.
The roots of the crisis go back to the decades after World War II. During the war, shortages of oil and gas pushed Japan to rely heavily on forests as a source of fuel for homes and industry. This led to widespread deforestation, leaving mountains around major cities such as Tokyo, Osaka and Kobe stripped of trees.
Noriko Sato, a forestry researcher and professor at Kyushu University in Fukuoka, said many of Japan’s mountains became barren after the war, creating disasters in several regions. She added that large-scale reforestation was carried out through publicly funded works to prevent soil erosion.
To restore forests quickly, the government turned to two native, fast-growing evergreen trees that could cover land rapidly and later provide timber for construction: Japanese cedar, known as sugi, and Japanese cypress, known as hinoki.
Today, sugi and hinoki plantation forests still cover about 10 million hectares, or roughly one-fifth of Japan’s total land area.
The problem is that both trees produce large amounts of light pollen, which can be carried easily into cities. Because many plantations were built up with the same tree types, pollen is released in heavy waves at the same time, making sugi and hinoki major drivers of Japan’s seasonal allergy crisis.
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