Reference; https://mbp-japan.com/jijico/articles/32482/
Modified and translated by CFJA
Experiencing a Japanese Summer for the First Time in 30 Years
From July 14, I spent two weeks in Japan. It was my first time returning to Japan during the summer in nearly 30 years.
Although I have lived in Toronto for almost 40 years, where temperatures occasionally exceed 30°C (86°F), the summer heat I experienced in Japan was far more intense than I had anticipated.
Daytime temperatures frequently rose above 35°C (95°F), and in some areas they even exceeded 40°C (104°F). It wasn’t just the high temperatures—it was also the humidity. Even a short time outdoors left me drenched in sweat and feeling as though my energy was being quickly drained.
This visit reminded me how completely my body has adapted to Toronto’s relatively mild summers. Even when the temperature exceeds 30°C, the physical burden feels very different in Toronto than it does in Japan.
When we live in the same climate for many years, our bodies gradually adapt to that environment. The way we perceive and respond to heat and cold changes over time. The Japanese summers that never seemed particularly challenging when I was younger now require much more careful attention to conserving my energy and maintaining my health.
Some time ago, I wrote an article about Summer Doyo—the traditional seasonal transition period—and how lifestyle habits during this time can help prevent summer fatigue. After experiencing a Japanese summer again for the first time in three decades, I was reminded firsthand of just how important those recommendations are.
With that in mind, I would like to share that article again.
What Is Summer Doyo in Traditional East Asian Medicine?
In traditional East Asian philosophy, the transitional period between seasons is called Doyo (土用). Doyo refers to the 18 days immediately preceding the beginning of each season according to the traditional Japanese calendar: Risshun (Beginning of Spring), Rikka (Beginning of Summer), Risshu (Beginning of Autumn), and Ritto (Beginning of Winter). Since there are four seasonal transitions each year, there are also four Doyo periods: Spring Doyo, Summer Doyo, Autumn Doyo, and Winter Doyo.
According to the 2026 calendar, the Doyo periods are:
- Winter Doyo: January 16 – February 3 (before Risshun, February 4)
- Spring Doyo: April 17 – May 4 (before Rikka, May 5)
- Summer Doyo: July 20 – August 6 (before Risshu, August 7)
- Autumn Doyo: October 20 – November 6 (before Ritto, November 7)
In Western medicine, organs are viewed primarily as anatomical structures. In Traditional East Asian Medicine, however, the Zang-Fu (Five Zang and Six Fu) system refers not only to the organs themselves but also to their physiological and functional relationships throughout the body.
According to this traditional theory, the Liver is associated with spring, the Heart with summer, the Lung with autumn, the Kidney with winter, and the Spleen is especially active during each Doyo period.
For this reason, Doyo is regarded as a time when the Spleen system—including digestive functions represented by the spleen and stomach—is under greater physiological demand. Irregular eating habits, overeating, or excessive physical strain during this period may place additional stress on digestion and reduce the body’s overall vitality.
From July 20 to August 6, Summer Doyo often coincides with the end of the rainy season in eastern Japan. Traditionally, this was the time for Doyo-boshi, the custom of airing books, clothing, and household items in the strong summer sunshine to remove moisture accumulated during the rainy season. The sun-drying of umeboshi (pickled plums) and the agricultural practice of nakaboshi, temporarily drying rice paddies, are also important seasonal traditions during this period.❶❷ Summer Doyo marks the transition from the damp, overcast rainy season to the powerful midsummer sunshine.
Summer Doyo also overlaps with Taisho (Great Heat), the hottest solar term of the traditional Japanese calendar.❸ In 2026, Taisho falls on Thursday, July 23. Around this time, the rainy season ends across much of Japan, and the country enters the hottest part of the year. It is also a season when many people begin to experience a loss of appetite.
Perhaps the best-known Summer Doyo tradition is eating unagi (freshwater eel) on the Day of the Ox during Summer Doyo (July 26 in 2026). Contrary to popular belief, this custom is generally attributed not to Sugawara no Michizane but to Hiraga Gennai, an Edo-period scholar and inventor, who is said to have promoted eel as a nutritious food to help people endure the summer heat. Among the four Doyo periods, Summer Doyo is probably the one most familiar to the Japanese public.
How we spend the Doyo period can have a significant impact on our health. Healthy habits during Summer Doyo may help prevent summer fatigue, while neglecting our health during this seasonal transition may contribute not only to summer fatigue but also to seasonal fatigue during the colder months.
Is Summer Doyo Becoming the Beginning of Extreme Heat?
In recent years, Japan’s summers have become increasingly severe. On April 17, 2026, the Japan Meteorological Agency officially introduced the new term “Extreme Heat Day” (Gokusho-bi) to describe days when the maximum temperature reaches 40°C (104°F) or higher.❹
Many people expected the intense heat to arrive earlier this year, but temperatures remained relatively moderate throughout May and June. Then, beginning on Thursday, July 9, temperatures rose sharply across much of the country. People who have not yet become heat-acclimatized are at a greater risk of developing heat-related illnesses, making it important to begin preventive measures as soon as possible.❺
While Spring Doyo is characterized by rapidly increasing humidity and fluctuating temperatures, Summer Doyo is distinguished by persistent heat and high humidity. It is one of the most physically demanding periods of the year, making Summer Doyo an ideal time to prepare both the body and mind for the weeks of intense heat that lie ahead.
On the traditional calendar, Summer Doyo ends with Risshu (the Beginning of Autumn). Although the name suggests cooler weather, this is actually when Japan’s hottest weather often continues. In recent decades, the hot season has become noticeably longer. Over the past five years in Tokyo, days with maximum temperatures exceeding 30°C (86°F) have typically occurred from mid-May through mid-October—approximately three weeks longer than they did 70 years ago.❻❼
The way we experience heat also varies depending on where we live. Coastal regions often feel cooler because of sea breezes, whereas urban areas tend to be much hotter due to the urban heat island effect.❽ Concrete and asphalt absorb heat during the day and continue releasing it throughout the night, preventing temperatures from dropping after sunset. Over the past century, Japan’s average temperature has increased by about 1.2°C, while the average temperature in Tokyo has risen by approximately 3°C, illustrating how urbanization amplifies warming.
In cities, tall buildings also block natural airflow, allowing heat and humidity to accumulate and increasing the perceived temperature. Meteorologists have also suggested that El Niño conditions may contribute to above-average summer temperatures in 2026.❾❿
For these reasons, today’s Summer Doyo may no longer represent “the end of summer,” as it once did. Instead, it may be more accurate to think of it as the beginning of the season’s most extreme heat.
References
- Shin Nippon Calendar – Koyomi Seikatsu: Introduction to Doyo-boshi (Traditional Seasonal Airing)
- Kubota – Nakaboshi (Mid-Season Rice Field Drying)
- tenki.jp – Taisho (Great Heat): Understanding the Hottest Solar Term of the Year
- Japan Meteorological Agency – Introduction of the Term “Extreme Heat Day” (40°C or Higher)
- Could Excessive Cooling Be the Cause of Summer Fatigue? Is Summer Exhaustion Related to Cardiac Fatigue?
- Japan Meteorological Agency – Historical Weather Data
- WeatherX – Is Summer Becoming Longer?
- Japan Meteorological Agency – Urban Heat Island: Overview and Explanation
- Tokyo Metropolitan Government – Guide to Summer Heat Countermeasures
- Japan Meteorological Agency – El Niño and La Niña
- Weathernews – Why People Choose Shaved Ice Instead of Ice Cream Above 34°C
- TV Osaka – Summer Special: Refreshing Kakigōri
- Fukuoka Pharmaceutical Association – Questions and Answers on Indoor Climate
- Weathernews – Pollen Inside (Referenced Climate Data)
- Why Does Heatstroke Often Occur Indoors? The Importance of Air Conditioning
- Is Your Sense of Temperature Normal? How to Maintain Healthy Thermosensation?