Reference; https://mbp-japan.com/jijico/articles/32482/
Modified and translated by CFJA
Ice Cream or Shaved Ice?
Once the outdoor temperature rises above 30°C (86°F), most people become much more aware of the heat. This is also around the point at which the risk of heat-related illness begins to increase. When temperatures remain above 35°C (95°F)—approaching or even exceeding normal body temperature—the body’s natural ability to dissipate heat gradually becomes less effective.
As temperatures rise, the body produces large amounts of sweat in an effort to cool itself. At the same time, people naturally seek relief by using air conditioning and consuming cold foods and beverages. Sales of ice cream and shaved ice (kakigōri) increase dramatically from mid-July through mid-August, closely paralleling rising outdoor temperatures.
Interestingly, consumer preferences appear to change when the daily maximum temperature reaches approximately 34°C (93°F). At lower temperatures, people tend to choose ice cream, which contains milk fat and air and is typically served at around −7°C (19°F). As temperatures climb higher, however, many people switch to kakigōri, made from finely shaved pure ice and served at approximately 0°C (32°F). This may reflect the body’s instinctive desire for a stronger cooling effect during periods of extreme heat.⓫⓬
However, excessive consumption of very cold foods and drinks may suppress the body’s natural ability to release heat, potentially interfering with normal temperature regulation. For this reason, moderation is important.
During heavy sweating, blood flow is redirected toward the skin to facilitate heat loss. As a result, relatively less blood is available for the digestive organs. When the stomach and intestines are already functioning less efficiently, consuming excessive amounts of cold or water-rich foods and beverages can further impair digestion, contributing to summer fatigue. As overall physical strength declines, the body also becomes less efficient at dissipating heat, increasing the risk of heat-related illness.
To stay healthy throughout Summer Doyo, it is important to promote effective heat dissipation while using air conditioning appropriately, rather than relying solely on cold foods and drinks to stay cool.
What Is the Ideal Air Conditioning Temperature?
What is the ideal air conditioning temperature that keeps you comfortable without placing unnecessary stress on your body?
In general, the recommended indoor environment during summer is a temperature of 25–28°C (77–82°F) with a relative humidity of 50–60%.⓭ Setting your air conditioner within this range can help maintain comfort while supporting your body’s natural ability to regulate its temperature.
During August, outdoor temperatures typically begin to rise around 11:00 a.m., peak at approximately 2:00 p.m., and remain high until around 5:00 p.m. Indoor temperatures, however, often peak about one hour later, around 3:00 p.m., and may stay elevated until 7:00 p.m. Running your air conditioner appropriately during these hours is especially important to reduce heat stress indoors.
One point that deserves attention is that remaining in an excessively cold room for prolonged periods may reduce your body’s ability to adapt to heat. Our bodies maintain their heat tolerance through repeated exposure to warm environments. If we constantly stay in overly cooled spaces, this natural adaptation can gradually decline.
Survey data from different regions of Japan also illustrate how people perceive heat differently. In most areas, people report feeling “hot” when temperatures approach 30°C (86°F). In Hokkaido, however, the average threshold is only 25.9°C (78.6°F). Because Hokkaido has a climate more similar to Toronto—with lower humidity and generally milder summer temperatures—people living there become uncomfortable at lower temperatures. This situation is similar to spending all day in an overly air-conditioned environment, where the body gradually becomes less accustomed to summer heat.
In regions where daytime temperatures frequently exceed 30–35°C (86–95°F), it is important to avoid excessive cooling until the weather begins to moderate, often around October. Maintaining a reasonable balance between cooling and natural heat exposure may help reduce the risk of summer fatigue after the Summer Doyo period.⓮
If your home tends to become excessively hot, the following measures may also help:
- Block direct sunlight with curtains, blinds, or shades.
- Open the windows briefly in the morning to improve ventilation before outdoor temperatures rise.
- Use a circulating fan to improve airflow while avoiding direct exposure to cold air from the air conditioner.
Improving indoor air circulation can also help lower indoor temperatures during the evening and early morning, making your living environment more comfortable while reducing the need for excessive cooling.
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?