Walk through a Japanese city on a clear day in early March. You see the same scene on every train platform. Masks cover most faces. Many people wear wraparound glasses, and tissues come out the moment the doors open. This is sugi pollen allergy at work. It comes from one tree. That tree was planted across the country in huge numbers after the war.
The short answer is scale. Japanese cedar pollen floods the air each spring. Japan covered its hills with sugi trees on purpose, and those trees are now old enough to shed clouds of pollen. The tree itself is not unusual. The sheer number of them is.
After World War Two the government pushed a huge tree-planting program. The goal was to rebuild timber for housing and fuel. Crews planted sugi across millions of acres of mountain slopes. The tree grows fast and straight, so it was an easy pick. Then cheap imported lumber undercut the market. Many of those forests were never cut. The trees just kept growing.
A sugi tree starts to make heavy pollen once it passes 30 years of age. Most of the post-war forests crossed that line decades ago. So the timing was almost guaranteed. Each spring the small male cones swell, dry out, and burst open. A single mature stand can release huge volumes of pollen that drift for miles on the wind. A whole hillside of these trees turns the sky a faint yellow on the heaviest days.
The health toll is well documented. One peer-reviewed study counted how many people react. More than one third of Japanese people now have a sugi pollen allergy. You can read the data in a journal known as the Journal of Allergy and Clinical Immunology. The rate of sugi pollinosis climbed fast. It went from 11.7% in 1998 to 38.8% in 2019. The worst stretch runs from February through April each year.
Sugi pollen is light and dry, so it travels long distances on dry, windy spring days. Cities far from any forest still get heavy pollen counts because the grains ride the wind in from the hills.
The medical name for it is sugi pollinosis. You feel it as sneezing, a runny nose, and itchy, watering eyes. It is the same hay fever you might feel from grass or ragweed at home. The difference in Japan is the sheer dose. Millions of trees release pollen at once. Even a mild case can knock you flat.
The timing makes it worse. Sugi trees all share the same release window. So the pollen comes out in one short, heavy burst rather than a slow trickle. A hot summer the year before pushes the next count higher, since heat helps the trees set more cones. People in Japan watch the daily pollen forecast the way you might watch the rain forecast. They plan errands and laundry around it.
Here is the part that matters for your own yard. A single sugi tree is a far smaller pollen source than a plantation. One landscape tree gives off a tiny fraction of what a hillside of cedars puts into the air. Japan's problem grew out of mass planting across whole mountain ranges. Your one tree sits at the opposite end of that scale.
You can keep your own tree quiet, too. Pick a cultivar bred to make few male cones, and you cut most of the pollen before it ever forms. You can also shear off the small cones in late autumn before they mature. That stops the rest at the source. The lesson from Japan is about planting one species across a whole country. A single cedar in your garden still earns its place.
Read the full article: Japanese Cedar: Complete Care and Growing Guide
