Japan’s Hay Fever Crisis: A Legacy of Postwar Reforestation and a Warming Climate

Nearly half of Japan’s population suffers from hay fever, a condition increasingly linked to the country’s vast cedar and cypress plantations. What was once a relatively uncommon ailment has become a significant social issue, prompting government action and scientific research to address its root causes.

The Rise of Hay Fever in Japan

Hay fever in Japan, known as kafunshō (花粉症), is primarily triggered by pollen from Japanese cedar (Cryptomeria japonica, or sugi) and Japanese cypress (hinoki). According to a 2019 Ministry of the Environment report, 42.5% of Japanese people experience some form of hay fever, with 38.8% specifically affected by cedar pollinosis.

The surge in hay fever cases is a relatively recent phenomenon. Prior to the 1960s, pollen allergies were rare in Japan. However, the postwar period saw a dramatic shift in the country’s forests, laying the groundwork for today’s widespread problem.

Postwar Reforestation and its Unintended Consequences

Following World War II, Japan embarked on a large-scale reforestation campaign. Vast areas of forest land, decimated during the war to supply the military, were replanted with fast-growing conifers like cedar and cypress to meet the booming demand for timber in the postwar housing boom.

In 1964, the liberalization of trade in forest products led to cheaper timber imports, diminishing the economic incentive to maintain domestic forestry. Many plantations were left unmanaged, allowing the trees to mature and produce increasing amounts of pollen. By 2000, over 85% of cryptomeria trees were over 20 years aged, and more than 60% were over 30 years old, significantly increasing pollen production.

A Warming Climate Exacerbates the Problem

Recent data suggests that the 2026 hay fever season may be particularly intense. Weathernews, a weather information company, predicts that the pollen count across Japan will be 28% higher than average this year, with some prefectures, like Akita, potentially seeing pollen levels six times higher than last year.

This increase is attributed, in part, to the extreme heat experienced in Japan during the summer of 2025, which promoted the growth of male flowers responsible for pollen production. Cedar flower buds form during the previous summer, and warmer, sunnier conditions tend to result in heavier pollen loads the following spring.

Government Initiatives and Research Efforts

Recognizing the scale of the problem, the Japanese government has declared “war on hay fever.” A decade-long program has been launched to reduce pollen production at the source, focusing on cutting older trees and replanting forests. The goal is to reduce pollen-producing cedar in planted forests by 20% nationwide by 2033.

Key components of the initiative include:

• Accelerating the harvesting and replanting of aging cedar stands.
• Increasing annual harvesting to around 70,000 hectares by fiscal 2033.
• Expanding demand for cedar timber to 17.1 million cubic meters per year.
• Raising the share of low-pollen cedar seedlings to over 90% of total production.

Researchers are also developing low- and no-pollen cedar varieties and testing pollen suppressants, including a spraying agent using fungal spores that parasitize cedar male flowers.

Challenges Remain

Despite these efforts, significant challenges remain. A dwindling forestry workforce and the complex ownership of forest land – with a substantial portion having unclear or untraceable owners – hinder effective forest management. Approximately 32% of forest land in some rural areas has not had its ownership updated in over 50 years, and around 30% has owners who cannot be contacted.

Addressing the hay fever crisis requires a multifaceted approach, combining government policies, scientific innovation, and community involvement to revitalize Japan’s forests and mitigate the impact of pollen on public health.