Heatstroke (Netchusho) in Japan
Heatstroke in Japan is a summer routine risk, not a freak event. Humid heat disables sweating, and the 熱中症 (netchūshō, "heatstroke") count climbs every July.1
Procedures, fees, and requirements can change. Confirm current details at the Fire and Disaster Management Agency heatstroke reports and the Environment Ministry heat information site. This article is general information, not medical advice; for symptoms or a complex case, consult a licensed physician.
Overview
In the week through July 19, 2026, ambulances carried 10,857 heatstroke patients to hospitals across Japan, 2.4 times the prior week, with 14 deaths and 321 severe cases (as of July 19, 2026; confirm current figures with the Fire and Disaster Management Agency).12 The 2025 season set the record at more than 100,143 transports from May to September (as of October 2025; confirm current figures with the Fire and Disaster Management Agency).3 Prevention is therefore a daily summer habit, and this article owns that habit without repeating clinical manuals.
Why Japanese Summers Turn Dangerous
Heat alone is manageable. Heat plus Japan's humidity is not, because sweat stops evaporating and core temperature climbs.
Humidity Is the Multiplier
Sweat cools only when it evaporates, and saturated air blocks evaporation. Indoor rooms without airflow turn just as dangerous as sunny streets, which is why the Fire and Disaster Management Agency urges air-conditioner use and frequent breaks alongside hydration.1
Who Is Most Vulnerable
Older residents dominate the statistics: 6,734 of the 10,857 patients in the July 2026 record week were 65 or older, over 60 percent (as of July 19, 2026; confirm current figures with the Fire and Disaster Management Agency).2 Children under 7, outdoor workers, athletes, and residents without air conditioning face elevated risk. Residences were the most common onset location at 4,523 cases, ahead of streets and outdoor venues.2
Warning Signs
Early Signs
Heavy sweating with dizziness, nausea, or headache marks heat exhaustion sliding toward danger.4 Move to a cool place, loosen clothing, and start electrolytes at this stage. Do not try to push through an outdoor task.
Emergency Signs
Sweating that stops despite the heat, confusion, fainting, or very high body temperature means calling 119 at once.4 Tokyo's 2025 summer included one death and 47 critical cases among 8,341 transports from June through August (as of September 2025; confirm current figures with the Tokyo Fire Department).4
These signs mean the body's cooling has failed. Cool the person with whatever is at hand, keep them still, and call 119 rather than driving them yourself.4
Prevention Checklist
Hydration With Electrolytes
Drink before thirst arrives, and make sustained sweating an electrolyte job: 経口補水液 (keikō hosui eki, "oral rehydration solution") products such as OS-1 and Pocari Sweat replace the salts that plain water does not. Keep a bottle at the bedside as well as in the work bag, since indoor night cases are common.12
Indoor Temperature Management
Run the air conditioner whenever the indoor temperature passes 28 degrees, without rationing, and budget for the higher summer electricity bill as a health expense.1 Add a fan for airflow and a dehumidifier for the humidity half of the problem. The bill is the cheapest part of this article.
Decide by the room reading, not by the calendar or by how neighbors manage. If the indoor display reads above 28 degrees, the air conditioner goes on.1
Outdoor Timing
Keep strenuous outdoor activity out of the 11am to 3pm window in July and August. Shift runs, matches, and heavy errands to early morning or evening, and take shaded breaks on a fixed schedule rather than when symptoms start.
The High-Risk Season and Official Alerts
The season runs June through September with an August peak; Tokyo's July 2025 count of 3,439 was its worst month (as of September 2025; confirm current figures with the Tokyo Fire Department).4 The joint Environment Ministry and JMA Heat Stroke Alert (熱中症警戒アラート, netchūshō keikai arāto) covers 58 regions and goes out at 5pm the prior day and 5am the same day whenever WBGT (暑さ指数, atsusa shisū, "heat index") of 33 or higher is forecast (as of current MOE practice; confirm current criteria with the Environment Ministry).56 A prefecture-level special alert tier covers unprecedented heat, with revised operations running in 2026 (as of April 2026; confirm current criteria with the Environment Ministry).7 Alerts rose sharply in the 2024 season, which also used the 33 threshold (as of the 2024 season; confirm current criteria with the Environment Ministry).8
| Period | Transports | Note |
|---|---|---|
| Week through July 19, 2026 | 10,857 | Record 2026 week; 14 deaths, 321 severe |
| May to September 2025 | 100,143 | All-time seasonal record |
| Tokyo, June to August 2025 | 8,341 | Tokyo record since 2010 |
The table rows carry their as-of dates in the surrounding prose. All figures come from Fire and Disaster Management Agency weekly and seasonal reports via NHK, Jiji, and the Japan Times.1234
Good to Know
The electricity bill is cheaper than the ambulance ride
Rationing air conditioning to save money is the classic trap, and residences lead onset locations. Treat summer cooling as a fixed health cost from June, the way winter heating already is; the alternative is priced in an ER visit.12
Indoor cases outnumber outdoor cases
People guard against the sun and forget the kitchen, the bath, and the unventilated bedroom. Ventilate and cool the rooms where you spend hours, not just the moments you step outside.2
Oral rehydration drinks are pharmacy stock, not vending-machine stock
OS-1 sits in pharmacies and drugstores, often near nursing-care supplies rather than sports drinks. Buy a few bottles before the hot weeks so they are already home when early signs appear.1
See also
- Calling 119: When and How
- What to Bring to the ER
- What an ER Visit Actually Costs in Japan
- Emergency Hospital Tiers in Japan
- #7119 Japan: Non-Emergency Medical Advice
- Volcanic Ash and Air Quality in Japan