Why Is Pollen Allergy So Common in Japan? Cedar Pollen, Forest History, and How Hay Fever Happens

Last updated: 2026-03-08

Japan’s pollen problem is not just a matter of “spring allergies.” It is tied to forest history, postwar reforestation, regional planting patterns, and the way the immune system reacts to repeated exposure. For travelers, this matters because Japan’s spring can be beautiful and miserable at the same time: cherry blossoms and cedar pollen often arrive in the same broad season. The goal of this page is to explain both sides of the issue — why pollen is such a big problem in Japan, and what is actually happening inside the body when hay fever symptoms start.

Why Japan has such a big pollen problem

One major reason is historical. After World War II, Japan needed large amounts of timber for reconstruction, and logged areas were rapidly reforested. According to the Forestry Agency’s annual report, planted forests such as cedar forests were intensively established from the 1950s to the 1970s, and the area of planted forests increased from about 5 million hectares in 1949 to about 10 million hectares today. Cedar became the main forestry species, accounting for about 40% of that planted-forest total.

That would not automatically have created today’s allergy burden, but time changed the picture. The same Forestry Agency report explains that one likely reason pollen dispersion increased is that the area of cedar forests aged 20 years and above — the stage at which they begin producing male cones — increased as these planted forests matured. In other words, Japan did not simply plant many cedar trees; it also ended up with large areas of pollen-producing cedar forests at the same time.

The result is now large enough to be treated as a national social issue. The Forestry Agency’s recent annual report says cedar pollen is the most common cause of pollen allergy in Japan and that about 40% of the population suffers from cedar pollen allergy every spring. The government has responded by strengthening pollen-source reduction measures, with goals including reducing the area of pollen-source cedar forests by 20% in 10 years and halving pollen emissions in about 30 years.

What is Japanese cedar pollen, and why is it such a problem?

The main culprit is Japanese cedar (Cryptomeria japonica), often called sugi in Japan. Japanese cypress (hinoki) is also important. The Forestry Agency notes that cypress often causes allergy alongside cedar because the two species are in the same family and their pollen has similar allergens. It also notes that cypress is commonly planted in western Japan, which helps explain why cedar-and-cypress season can be especially difficult in parts of western Japan.

In Tokyo, official allergy guidance says the cedar and cypress pollen season runs from February to early May, with cedar usually peaking in March and cypress in April. The same Tokyo guidance says pollen tends to be heavier on warm days, on the first sunny day after rain, and on sunny, windy, dry days. That is one reason spring in Japan can feel unpredictable: even within the same week, conditions can swing from manageable to miserable.

Cedar and cypress are not the only pollen triggers in Japan. Tokyo’s official allergy guidance also says that grasses, ragweed, and mugwort can trigger symptoms later in the year, especially from summer to autumn. So “hay fever in Japan” does not end neatly with cherry blossom season, even though spring cedar pollen gets the most attention.

Why hay fever happens: IgE, mast cells, and histamine

Hay fever is an IgE-mediated allergic reaction. In allergic rhinitis, the immune system treats otherwise harmless airborne material — such as pollen — as a threat. A modern review of allergic rhinitis explains that the allergic response has an early phase and a late phase. In the early phase, after allergen exposure, IgE already bound to high-affinity receptors on mast cells is cross-linked, which activates the mast cells and triggers rapid mediator release.

This is where mast cells become central. Mast cells in the nasal mucosa release mediators such as histamine, along with other inflammatory signals. Reviews of allergic rhinitis explain that this early-phase histamine release is a major reason people quickly develop sneezing, runny nose, itching, and eye symptoms after pollen exposure. In simple terms, pollen is not “damaging” the nose like sandpaper; the body is overreacting to it.

The reaction does not end there. During the late phase, additional inflammatory cells — including eosinophils, Th2 cells, and other immune cells — are recruited into the nasal mucosa. This later wave of inflammation is one reason symptoms can persist beyond the first burst of sneezing and itching, and it helps explain why nasal congestion can become stubborn and heavy even after the initial exposure.

Why symptoms can feel worse over time

At the population level, the Forestry Agency notes that prevalence has risen over time: cedar pollen allergy in Japan was first reported in 1964, and nationwide epidemiological surveys estimated that prevalence increased from 16% in 1998 to 39% in 2019. The report adds that one major reason for this long-term increase is that once hay fever develops, symptoms rarely disappear naturally, so the number of sufferers accumulates over time.

At the individual level, allergic rhinitis can also become more burdensome because repeated exposure keeps reactivating this inflammatory cycle. Reviews of allergic rhinitis describe how mast-cell activation, mediator release, and late-phase recruitment of inflammatory cells can sustain symptoms and contribute to ongoing nasal inflammation. That is part of why someone may start with “just sneezing in spring” and later feel that the season brings heavier congestion, stronger eye symptoms, or a lower threshold for reacting.

This is also why treatment timing matters. Tokyo’s official allergy FAQ says that some medicines work better when started on the predicted pollen start date or even about a week before that point for certain drugs. That advice makes sense biologically: once the inflammatory cascade is fully underway, it is harder to pretend the season has not started.

Why Hokkaido can feel different

Hokkaido is often easier for travelers whose main trigger is cedar pollen, but it is not allergy-free. The Forestry Agency explicitly says that in Hokkaido, many people suffer from pollen allergy caused by birch and grass because there are few cedar trees there due to the cold climate. So switching from Honshu to Hokkaido may reduce cedar exposure, but it does not mean the sky becomes harmless for everyone.

That distinction matters because travelers sometimes hear “Hokkaido has less cedar pollen” and translate it into “Hokkaido has no pollen problem.” That is too simple. The better way to think about it is this: Hokkaido often has a different pollen profile, not the total absence of seasonal allergy triggers.

What this means for travelers

For travelers, the practical lesson is not just “bring antihistamines.” It is that Japan’s pollen problem has structure. If you are sensitive to cedar or cypress pollen, spring travel in much of Honshu can be harder than the photos suggest. If you are sensitive to other pollens, symptoms may continue beyond spring. If you already know that you get strong seasonal symptoms, it makes sense to check local pollen conditions before your trip, prepare medicines early, and think about season choice rather than relying on luck.

This is also why the site’s more practical pages matter. A background page like this one explains why Japan has such a visible pollen problem. The next step is the practical question: when the season hits, what should you actually do, and when should you change your plans, start treatment, or seek care? That is where your symptom-focused and forecast-focused pages come in. This last sentence is an editorial recommendation based on the relationship between the official pollen season data and the medical mechanism described above.

FAQ

Why is cedar pollen such a big issue in Japan?

Because Japan planted large areas of cedar after World War II for reforestation and timber production, and many of those forests later matured into pollen-producing stands. The Forestry Agency identifies cedar as the main forestry species in planted forests and the most common cause of pollen allergy in Japan.

Is Japanese cypress part of the same problem?

Yes. Japanese cypress is another major spring pollen source, especially in western Japan, and the Forestry Agency notes that cypress often causes allergy alongside cedar because their pollen has similar allergens.

Why do symptoms start so quickly?

Because the early allergic response is driven by mast cells that already have allergen-specific IgE bound on their surface. When pollen cross-links that IgE, mast cells release histamine and other mediators within minutes, producing rapid symptoms such as sneezing, itching, and runny nose.

Why does nasal congestion often last longer?

Because allergic rhinitis also has a late inflammatory phase. Reviews describe recruitment of eosinophils, Th2 cells, and other inflammatory cells into the nasal mucosa, which helps sustain inflammation and makes blockage and swelling linger beyond the first wave of symptoms.

Does Hokkaido solve the pollen problem?

Not completely. Hokkaido has few cedar trees, so it can be easier for people whose main trigger is cedar pollen, but the Forestry Agency says birch and grass pollen are important there.

Official sources

– Forestry Agency, Ministry of Agriculture, Forestry and Fisheries (Japan): Annual Report on Forest and Forestry in Japan (FY2023, summary)
https://www.maff.go.jp/e/data/publish/AnnualReportonForestandForestry/Part1_AnnualReportonForestandForestryinJapan_FY2023_1.pdf

– Tokyo Metropolitan Government: Tokyo Allergy Information Website — The basics (allergic rhinitis / hay fever)
https://www.hokeniryo1.metro.tokyo.lg.jp/allergy/en/knowledge/rhinitis_etc.html

– Tokyo Metropolitan Government: Tokyo Allergy Information Website — What to do
https://www.hokeniryo1.metro.tokyo.lg.jp/allergy/en/measure/rhinitis_etc.html

– Tokyo Metropolitan Government: Tokyo Allergy Information Website — FAQ
https://www.hokeniryo1.metro.tokyo.lg.jp/allergy/en/faq/rhinitis_etc.html

Medical background sources

– Allergic Rhinitis and its Pharmacological Treatment
https://pmc.ncbi.nlm.nih.gov/articles/PMC9021509/

– Histamine and histamine receptors in allergic disease
https://pmc.ncbi.nlm.nih.gov/articles/PMC6469109/

– Allergic rhinitis: the “Ghost Diagnosis” in patients with asthma
https://pmc.ncbi.nlm.nih.gov/articles/PMC9599528/