Boiling Point
How to prevent and respond to heatstroke in Japan this summer
A passerby holding a parasol wipes her face as she walks on the street amid a heatstroke alert in Tokyo and other prefectures, in Tokyo on July 9. | REUTERS
Staying hydrated and controlling the rise in one's body temperature are the fundamental ways for preventing and alleviating heat-related illnesses.
The climate change-driven rise in temperatures is increasing the health risks that come with Japan’s scorching summers, with on average around 1,300 people dying due to heat-related illnesses each year over the five-year period through 2022, according to health ministry data.
In the week through July 7 — part of what was meant to be the somewhat cooler rainy season — 9,105 people were transported to hospitals due to heatstroke, twice the number during the same period last year, according to the Fire and Disaster Management Agency.
To stay safe this summer, here’s what you need to know about heat-related illnesses as well as how to prevent, identify and treat them.
What are the health risks posed by extreme heat?
When somebody experiences an excessive loss of water and salt, heat exhaustion may occur. The condition is marked by symptoms such as a high body temperature, dizziness and a rapid heartbeat.
The much more serious heatstroke occurs when the body cannot cool itself properly due to extreme heat, high humidity, exercise or dehydration. Some early symptoms include dizziness, headache, slurred speech and vomiting, according to the Environment Ministry’s Heatstroke Environmental Health Manual.
When heatstroke occurs, the body’s temperature rises rapidly to 40 degrees Celsius and above. If not treated properly, heatstroke can cause loss of consciousness, damage to organs and disability. In some cases, it can be fatal.
What can you do to prevent and alleviate heat-related illnesses?
Fundamentally, measures to prevent these conditions include staying hydrated and controlling the rise in body temperature.
People should avoid exposure to high temperatures, for example by refraining from unnecessary exercise during hot days, staying in the shade and taking frequent breaks in cooler areas.
Level 1 patients should be moved to a cooler environment immediately to let their body temperature go down, and they should drink plenty of water.
When cooling someone down, the most effective way is to place cold wet towels, cold packs or ice on the head, neck, under the armpits, and groin.
The patient’s level of consciousness plays an important role in determining the level of severity.
When someone shows signs of altered consciousness, they are classified as Level 2 and should receive professional medical attention.
Level 3 applies to those that are unconscious.
Who is most vulnerable?
Elderly people, younger children, pregnant women and people with existing health conditions such as obesity or reduced heart, lung or kidney functions are especially vulnerable to heatstroke. In addition, certain drugs that affect the autonomic nervous system or circulatory function, such as blood pressure medication, can also increase the risk of heatstroke.
Wearing loose-fitting, quick-drying clothing also helps the body to better cool itself down during hot days. Clothing made of black material should be avoided, as it absorbs more radiant heat than other colors.
Frequent drinking of water is also crucial to prevent dehydration. Drinking alcohol can be dangerous, as it affects the circulatory system and accelerates the dehydration process.
Meanwhile, air conditioning has a crucial role to play in reducing heat-related illnesses.
Research by the National Institute of Environmental Studies, University of Tokyo and the National Institute of Advanced Industrial Science and Technology published last year found that heat-related deaths in the month of August from 2000 to 2010 were reduced by 36% due to air conditioning (although these devices contribute to increased heat in the outside environment, with 3.1% of such deaths attributed to this). Under a scenario in which the average global temperature rises by 3 C, the reduction in deaths would be 47%.
For those without access to air conditioning, a revised climate change adaptation law that went into effect in April urges local municipalities to set up designated, indoor cooling shelters for use during extreme heat conditions. A complete list and map of such cooling shelters in Tokyo, for example, can be found on the metropolitan government’s website.
What should you do if someone has heatstroke?
The Japanese Association for Acute Medicine classifies heatstroke into three levels of severity based on the “need for specific treatment.”
Level 1 consists of mild symptoms that can be managed with first aid on-site. Those with moderate symptoms and needing to see a health care professional are classified as Level 2. The highest level is for severe symptoms that require hospitalization and intensive treatment.
Passersby take a break under a cooling mist amid a heatstroke alert in Tokyo and other prefectures, in Tokyo on July 9. | REUTERS
Older people tend to sweat less than younger people, and are more prone to dehydration. In addition, older people also tend to use air conditioning less often, or set a higher temperature when using it. From May to September 2023, a total of 91,467 people were transported to hospitals due to heatstroke, of whom 107 died. Almost 55% of those were age 65 and above, according to Fire and Disaster Management Agency data.
Younger children are also more vulnerable to excessive heat as body functions that serve to adjust body temperature, such as sweat glands, are not yet fully developed. In addition, the bodies of children have a larger surface area in relation to their body weight than those of adults, which make it easier for their body temperatures to rise in strong heat or under direct sunlight.
How can you know when heat represents a threat?
The Environment Ministry issues heatstroke alerts based on the wet-bulb globe temperature (WBGT), an index used to measure major environmental heat factors such as air temperature, radiant heat and humidity.
Heavy exercise should be avoided when the WBGT index is between 28 and 31, which carries a "severe warning." When the WBGT index exceeds 31 — classified as “danger” — all forms of exercise should be stopped, according to the ministry.
Although a WBGT temperature of 35 C is considered to be the limit of the human body’s ability to adapt to extreme heat, with prolonged exposure being fatal for even healthy people, some research has shown that the threshold could be significantly lower even for young and healthy adults.
Starting this year, an even more severe “special heatstroke alert” will be issued when the WBGT index is projected to hit 35 degrees Celsius or above the following day, which suggests “unprecedented dangerous heat conditions that could cause serious health problems.”
