Hay fever, which did not exist in the past, was first reported in Japan in 1961.
Since the initial report, the number of people suffering from hay fever has gradually increased, and it is now a common disease affecting one in two people.
First, let's discuss the history of hay fever in Japan and the current prevalence of the condition.

The history of hay fever in Japan

In Japan, the first report of ragweed pollen allergy was in 1961. Subsequently, a report of cedar pollen allergy was made in 1964.
During the Meiji era, it was confirmed overseas that hay could cause symptoms such as itchy eyes, sneezing, and a runny nose, but for some time after the war, there were hardly any reported cases of this condition in Japanese people.
After World War II, Japan planted a large number of cedar trees to be used as resources for reconstruction. However, when the trees were scheduled to be harvested, the availability of inexpensive imported timber led to delays in the felling of many of them.
As a result, large amounts of pollen are released from the remaining cedar trees, leading to an increase in the number of people suffering from hay fever caused by cedar pollen.

Furthermore, changes in air pollution and dietary habits in Japan over time have also contributed to the spread of hay fever, which did not exist in the past.

Currently, it is a national disease affecting one in two people.

The prevalence of allergic rhinitis, including hay fever, had risen to 49.2% by 2019, making it a national disease affecting one in two people. The prevalence of cedar pollen allergy is also on the rise, specifically as shown in the following table.

Item	Allergic rhinitis in general	Japanese cedar pollen allergy
1998	29.8%	16.2%
2008	39.4%	26.5%
2019	49.2%	38.8%

Age group	有病率
20 fee	47.5%
30 fee	46.8%
40 fee	47.5%
50 fee	45.7%
60 fee	36.9%

reference:
National Epidemiological Survey of Nasal Allergies 2019 (Comparison with 1998 and 2008): Preliminary Report - Targeting Otolaryngologists and Their Families -

The prevalence is high across a wide range of age groups, from those in their 20s to those in their 50s.
Hay fever, which is increasing year by year, can be considered a common national ailment.

The main reasons for the dramatic increase in hay fever, which was virtually nonexistent in the past, include the increase in pollen dispersal and the effects of air pollutants.
Other contributing factors include the Westernization of dietary habits and a decrease in infectious diseases, which will be explained in detail below.

Increase in pollen dispersal

The dramatic increase in hay fever, which was unprecedented in the past, is largely due to the growth of cedar and cypress trees planted after the war, which have increased the amount of pollen dispersed. Cedar pollen levels surged in 1979, 1982, and 1984, and large amounts were also observed in 1995.

Furthermore, pollen levels have continued to increase since 2000, and the prevalence of cedar pollen allergy is also on the rise.

Impact of air pollutants

Inhaling pollen that has been contaminated with chemicals in the air through your nose can increase the likelihood of an allergic reaction.
In Japan, cedar pollen accounts for about 7% of hay fever cases, but cedar trees have been growing here for a long time.
In the past, fewer people were affected by cedar pollen, but with the changing times, the number of cedar pollen allergy sufferers has increased. This is thought to be due to the combination of the increase in cedar trees and air pollution.

In fact, there is a theory that inhaling cedar pollen in its natural state is unlikely to cause an allergic reaction, but inhaling it after it has absorbed airborne pollutants makes allergic symptoms more likely.
There is a high possibility that particles emitted from diesel vehicles will adhere to airborne cedar pollen, and pollen collected in urban areas often has a high concentration of these attached particles on its surface.
The increased risk of inhaling pollen contaminated with air pollutants is likely one of the reasons for the dramatic increase in hay fever sufferers.

Westernization of the diet

A diet high in protein and fat may worsen allergic rhinitis.

In Japan, dietary habits are gradually becoming more Westernized, with increased consumption of livestock products, oils, and dairy products, while rice consumption is on the decline.
The microorganisms present in the intestines are easily influenced by food, and it is thought that the intestinal environment is changing along with the Westernization of dietary habits.

Since the gut environment plays a crucial role in immune function, it has been suggested that people may be more prone to allergic symptoms than when they were eating a diet centered on traditional Japanese food, which is considered to be nutritionally balanced and healthy.

Decrease in infectious diseases

While infections with tuberculosis and parasites have drastically decreased, the number of patients with allergic rhinitis has increased.
It is believed that improvements in the environment and healthcare system have made people less susceptible to infectious diseases, which can lead to changes in the balance of cells in the body and cause allergic reactions to pollen.
For example, one report suggests that type II helper T cells, which become activated after a person no longer contracts tuberculosis, may become dominant and potentially cause allergic symptoms.

Hay fever doesn't develop immediately upon exposure to pollen; it develops after a sensitization period and accumulation of allergens.
Furthermore, the time it takes for symptoms to appear varies from person to person, making it difficult to predict when the symptoms will develop.
This article provides a detailed explanation of the mechanism by which hay fever develops.

It develops after a sensitization and accumulation period.

The symptoms of hay fever, such as sneezing and a runny nose, are essentially a reaction in which the body identifies pollen that enters the nose as a foreign substance and tries to eliminate and neutralize it. However, this reaction is preceded by sensitization and accumulation.
Sensitization is the process by which individuals with an allergic predisposition develop antibodies that are compatible with the invading pollen. The sensitization period is the preparatory stage before the onset of hay fever.
Once antibodies are produced, the body enters an accumulation phase where the number of antibodies increases each time the body is exposed to pollen. When a sufficient amount of antibodies is accumulated, hay fever symptoms develop.

The timing of onset varies from person to person.

The time it takes for hay fever symptoms to develop varies from person to person; some people experience it within a few years, while others may take several decades.
However, in recent years, due to factors such as increased pollen dispersal and changes in the environment and diet, there has been an increasing trend of cases developing within a short period of time, and many children are now suffering from hay fever.

If you haven't yet been diagnosed with hay fever, understand that it could develop at any time, and seek medical attention promptly if you experience symptoms such as sneezing or a runny nose.

Avoiding bringing pollen indoors is key to preventing hay fever.
If you develop hay fever despite taking preventative measures, symptomatic treatment and immunotherapy are effective treatments.
We will explain the treatment options and prevention tips in detail.

Treatment methods for hay fever

For hay fever, symptomatic treatment using antihistamines and nasal steroid sprays is the mainstream approach, with the main goal being to suppress the symptoms caused by hay fever.
Furthermore, immunotherapy is also effective in preventing allergic reactions even if pollen enters the body.

There are two types of immunotherapy: sublingual immunotherapy and subcutaneous immunotherapy. Both involve regularly administering medication containing components that trigger an allergic reaction. Timing is crucial for immunotherapy; it must be administered during periods when pollen is not in the air.

Some medications require at least three years of treatment, so it's a good idea to consult your doctor about the treatment duration and expected effects before making a decision.

Tips for preventing hay fever

To prevent hay fever, it's important to keep pollen out of your nose.

Specifically, the following methods are effective:

• Wearing a mask or glasses
• Avoid going out around midday and in the evening when pollen is most likely to be dispersed.
• Utilize teleworking to reduce going out.
• Choose clothing that is less likely to attract pollen.
• Reduce exposure
• Wash your hands, gargle, and shower or bathe to wash away pollen.
• When opening windows for ventilation, use sheer curtains.
• Curtains should be replaced regularly.
• Avoid drying laundry outside.

If you can get cooperation from your workplace, it would be a good idea to avoid going out on days with high pollen counts and work from home instead.
If you cannot avoid going outside, we recommend choosing a time of day to go out, taking precautions to prevent pollen from sticking to your clothes, and washing off the pollen as soon as you get home.

The main reason for the dramatic increase in hay fever, which was virtually nonexistent in the past, is the increase in pollen dispersal. Changes in the environment and diet over time, as well as shifts in individual constitution, may also be contributing factors.
Hay fever doesn't develop immediately after pollen enters the nose; symptoms appear only after a certain amount of antibodies are produced and accumulate.

While the time it takes for hay fever symptoms to develop varies from person to person, the number of children developing hay fever is increasing.
If you haven't experienced any symptoms yet, try to avoid pollen as much as possible to prevent hay fever.
If you have developed symptoms, we recommend seeking treatment that is appropriate for you to alleviate your symptoms.