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The Strange Story of Hay Fever in Japan: Construction, Conspiracy Theories, Climate Change

The tale of Japan's national illness is intrinsically linked to the Japanese cedar. But there's much more to it than that.

By 8 min read

The history of hay fever in Japan is intrinsically linked to the Cryptomeria japonica. But to lay all the blame on the Japanese cedar tree misses some interesting parts of a story of the fortunes of modern living.

Japanese people often refer to hay fever as the national illness, or kokuminbyo (国民病). About a quarter of the population is estimated to suffer from it. That compares to just 8 percent of adults in the U.S., where it is simply referred to as a pollen allergy.

It wasn’t always this way. Hay fever was first reported here in 1964, the year of the Tokyo Olympic Games, when the nation sought to showcase its recovery from World War II defeat. Large pollen volumes in 1976, and again in 1979, promptly boosted the number of hay fever sufferers, and, as we entered the 1980s, the ailment was affecting so many people that it was regarded as a social problem.

The curse of the Japanese Cedar

Around 60 types of plants in Japan are recognized as causing hay fever, but by far the worst culprit – provoking symptoms such as sneezing, sore eyes, runny noses and more in a whopping 70 percent of sufferers – is the native cedar tree, or sugi (杉).

Despite its current role as the bad guy of Japanese hay fever, the cedar was a savior, of sorts, in post-WWII Japan when it was used to reforest mountains throughout the country that had been stripped bare by excessive logging during and after the war for use as fuel and lumber. Those treeless mountainsides had led to huge disasters and fatalities, particularly landslides, but the government-funded planting of the fast-growing cedars prevented any consequent large-scale damage.

Despite its current role as the bad guy of Japanese hay fever, the cedar was a savior, of sorts, in post-WWII Japan

Light, versatile, highly disease resistant, and due to its pencil-straight trunks, easy to process, cedar was also seen as the best choice for use as timber when demand for housing materials skyrocketed. In line with rapid growth in the Japanese economy following the government’s 10-year plan — a policy project launched in 1961 to boost the nominal national income — some natural diversified forest areas were also replanted with cedar.

As a result, even now, of the roughly 70 percent of the Japanese land mass that is covered in forest, around 40 percent is manmade according to the Japanese Forestry Agency. Artificially planted cedar forests make up 18 percent of the nation’s forests, while artificial native cypress trees, or hinoki (檜), make up around 10 percent. The unluckiest cedar hayfever sufferers also develop an allergy to cypress pollen, too.

In 1964, Japan’s lumber market was opened to cheaper, foreign imports and consumption of domestic timber dropped from roughly 90 percent to less than 30 percent. Turnover of the trees slowed and vast areas of cedar were left to mature to around 30 years of age when they began to produce pollen – in vast amounts.

Hayfever in the city vs. in the countryside

The main reason why Japan’s cedar and cypress trees cause hay fever is that there are just too many of them now, and therefore more of their pollen than our bodies can handle. However, the phenomenon of higher hayfever rates in cities, rather than rural areas surrounded by forests, suggests that there is more to the problem.

Figures show that hay fever symptoms are getting much worse as the years go on.

In a 2016 study on hay fever, the Tokyo government found that half of the capital’s residents have hay fever, roughly doubling from ten years earlier. It also showed that the ailment is growing among young children.

In a much older study from 2008 showing the percentage of hay fever sufferers by prefecture, Tokyo came in at just 13th place. Four of the top three spots were neighboring prefectures: Yamanashi to the west (topping the list at 44.5%) and Tochigi and Saitama prefectures to Tokyo’s north. One interpretation of the data compared it with locations of manmade cedar forests and concluded that areas downwind from the trees had the highest rates of hay fever. Pollen can travel on the wind for more than 100 kilometers, it noted.

There are other factors, too, that make hay fever worse in cities. Pollen that settles on concrete surfaces – unlike that which falls on natural ones and returns to the earth – soon rises again in the next breeze.

Studies on guinea pigs by Japan’s National Institute for Environmental Studies have found that high concentrations of diesel exhaust fumes, ozone or nitrogen oxide facilitate the onset of hayfever symptoms and worsen them. Other research has shown that air pollution breaks down the outer shell of pollen particles, releasing pollen powder small enough to enter our lungs. Although in their original, mountain-fresh form, the particles are big enough to be washed away by rain, that changes as they come into contact with pollution on their way into the city.

So what is Japan doing about hay fever?

In that 2016 study, the Tokyo Metropolitan Government asked sufferers what to do about the problem. The top answer in the multiple-choice survey was for the government to do research to find a cure for hay fever. In second place was to reduce the release of pollen by felling trees and trimming branches. Lastly, people asked for more information on the nature and prevention of hay fever and the release of seasonal pollen volume forecasts.

The top answer in the multiple-choice survey was for the government to do research to find a cure for hay fever

The government is busy working on all of these approaches.

Aiming to reduce pollen production, the national research body Forest Research and Management Organization, as of the end of 2017, had developed 142 varieties of low-pollen cedar and three no-pollen types, as well as 56 varieties of low-pollen cypress. Low-pollen varieties typically release less than 1 percent of the volume that regular trees produce.

More recently it has also developed a spray made from a natural fungus that can kill the pollen-producing male cedar flower within a few months. But it will take years until it can be widely used because researchers first need to confirm its safety for humans and for other vegetation.

A “magic pill” has also been developed that is said to eradicate cedar allergy symptoms in around 30 percent of users and reduce them in about another 50 percent.

Based on immunotherapy desensitization treatment, over a period of three years or more, patients place a pill under their tongue daily that releases a dose of the cedar pollen allergen. With a doctor’s prescription, the dosage is gradually increased so as to reduce the body’s sensitivity to pollen. It can be used by children as young as five.

Currently, though, the most common ways that Japan’s roughly 31 million hay fever sufferers try to reduce their symptoms is by wearing medical masks and hay fever goggles, and using eye drops, nose sprays, and oral medication, as well as air filters.

The Cedar Conspiracy

No, this isn’t a message from aliens, but the result of a forestry experiment into the relationship between tree growth and planting density that began in 1973 in Miyazaki Prefecture. The trees with the most space, at the outermost circle, have grown to a height of 20 meters, while those in the crowded center reach only 15 meters, creating an image of a huge concave head of broccoli and proving that density does affect growth.

Along with the logging industry, a lot of companies make a lot of money off the existence of Japan’s cedar forests. One estimate puts that cost at ¥40 billion. So it’s not surprising that there are whispers of conspiracy.

In 2015, in a debate program broadcast on nationwide television, the former governor of Miyazaki Prefecture – Japan’s leading producer of cedar timber – Hideo Higashikokubaru made comments saying, “there are people who profit from the hayfever industry,” and “if one tries to reduce the number of trees being planted, pressure is applied behind the scenes.”

Japan’s hayfever victims loved the idea and although a conspiracy theory may be too long a bow to draw, the government’s moves to end the nation’s springtime suffering are undoubtedly slow.

Looong-term goals

Japan’s Forestry Agency first developed a low-pollen cedar variety in 1996. It is, at last, planting such seedlings to replace cedar trees harvested in manmade forests. But if the current rate of replacement (6,400 hectares a year) continues, it will take about 700 years to replace the roughly 4.5 million hectares of those trees across the nation. Meaning that even to reduce pollen levels to 1960s levels would take well over 100 years.

 …to reduce pollen levels to 1960s levels would take well over 100 years

A rise in demand for Japanese cedar timber would consequently boost that replacement rate, and there are hopes that new techniques that reinforce the density of cedar timber to make it strong enough for use in buildings of around 10 stories may do that.

For now, the agency is prioritizing replanting in about 100,000 hectares of cedar forest that hit highly populated areas around Tokyo and Osaka with the most pollen.

The air that we share

Climate change is, of course, not making anything better. The World Allergy Organization says it is causing longer pollen seasons around the world and higher pollen production. “In every country, the prevalence of pollen allergy appears to be increasing,” according to the report.

As long as the causes of the problem remain, the symptoms will, too. And it seems clear that tackling the problem alone, whether individually or as a nation, will only do so much. Cleaning this air that we share is a project that needs to be tackled on a global scale. Amid stubborn inertia on changing away from fossil fuels, maybe hayfever is the Earth’s way of calling each of us to action.



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