Japan is famous for its spring pollen season, but "Asian dust" and "PM2.5" are two more threats you should not overlook.
Every year from March to May, these particles increase in the air and can cause sneezing, skin irritation, and even serious health concerns.
In this article, Mog breaks down everything you need to know — from the basics of Asian dust and PM2.5, to the weather conditions that make them worse, and the everyday precautions you can take to protect yourself.
In my previous article, I talked about pollen allergies.
This time, I'd like to explain "Asian dust" and "PM2.5" — two more things that spread through the air from March to May and can trigger allergies.
During this season, weather forecasts report on the spread of both pollen and these particles. Seeing footage on the news of the sky turning hazy and yellow is enough to make you sigh.
At our house, the car we had just washed ended up covered in dust again, and my skin broke out a little due to my allergies😭
🌏 What Is Asian Dust (Kosa)?
Asian dust refers to a natural phenomenon in which sand particles are swept up by strong winds from the deserts of China and Mongolia, then carried to Japan by the westerly winds. By the time the dust reaches Japan, it has absorbed not only sand but also chemical substances such as PM2.5, which is why it can trigger allergies.
💨 What Is PM2.5?
PM2.5 refers to extremely tiny particles that float in the air. "PM" stands for "Particulate Matter," and "2.5" means that the particles are 2.5 micrometers or smaller in size. The particles are made up of a variety of substances, including carbon, nitrates, sulfates, silicon, sodium, and aluminum.
💡 1 micrometer (μm) = one-thousandth of a millimeter. The width of a human hair is about 60–70 μm, which means PM2.5 particles are more than 25 times smaller — an incredibly tiny size.
Because PM2.5 particles are so small, they cannot be fully filtered out by the mucous membranes in the nose and throat, and they can reach deep into the lungs (the alveoli). They are said to carry the following health risks:
- Worsening of bronchitis and asthma
- Increased risk of heart disease and stroke
- Long-term cancer risk (recognized by the WHO)
Children, the elderly, and those with respiratory conditions need to be especially careful.
On days when "Asian dust" and "PM2.5" levels are high, try to avoid spending long periods of time outdoors. The precautions are the same as for pollen season.
While it is common in Japan to hang laundry outside to dry, it is best to avoid doing so on days when Asian dust and PM2.5 levels are elevated.
🌬️ Humidifying Air Purifiers
Air purifiers that can detect and automatically remove pollen and PM2.5 from indoor air are very popular in Japan.
In Japan, approximately 40% of households own an air purifier.
https://myel.myvoice.jp/products/detail/31007
Source: MyEL
Many models also come with a humidifying function. Since dry indoor air makes pollen more likely to circulate, it helps to keep humidity levels between 40–60%. My workplace has an air purifier with a humidifying function, and many people also keep a small personal humidifier on their desk. Since humidifying the air also helps keep skin moisturized, it seems to be especially popular among women who are conscious about skincare.
🌤️ Weather Conditions When Asian Dust and PM2.5 Are More Likely to Spread
Asian dust and PM2.5 do not spread at the same level every day.
The amount that spreads can vary greatly depending on weather conditions, so it is important to check in advance.
Days that require extra caution include:
- ☔ The day after rain (especially when it clears up and becomes windy)
- 💨 Windy days and the day after the first strong spring wind (Haru Ichiban)
- 🌤️ Before and after a migratory high-pressure system passes through
- 🌡️ Warm afternoons when temperatures start to rise
Getting into the habit of checking pollen and dust forecast information before heading out — such as on Weather News — will help you enjoy spring with peace of mind.
📱 Check Forecast Information on Weather News!
It is a good idea to get into the habit of checking the Asian dust and PM2.5 forecast before going outside.
"Weather News," a widely used weather forecast service in Japan, allows you to check the Asian dust radar and pollen forecast for free.
🌐 Weather News (Asian Dust Radar)
Source: weather news
In addition to weather forecasts, you can find all the information you need for spring outings in one place — including pollen, Asian dust, and PM2.5 levels — making it incredibly convenient.
Whether you live in Japan or are visiting as a traveler, we highly recommend bookmarking it!🔖
Spring in Japan comes with many challenges — pollen, Asian dust, and PM2.5 — but there is no need to worry if you check the information in advance and take the right precautions.
If you spot someone wearing a mask in spring, they are probably taking steps to protect themselves too.
