Japan's summer combines high temperatures with very high humidity, making heat especially dangerous for outdoor workers, older adults, and anyone whose body has not yet adapted. This page provides workplaces and communities with the symptoms, first aid, emergency call procedures, and multilingual medical resources needed for prevention and response — drawn entirely from official Japanese sources.
Last reviewed: June 1, 2026 / Reviewed by WELD Consulting Group occupational physicians
Japanese summer combines high temperatures with humidity of 70–80% for weeks at a time. When humidity is this high, sweat doesn't evaporate well, so the body can't release heat. Body temperature stays high, and heatstroke risk climbs sharply. The 2026 forecast also points to a hotter-than-average summer nationwide[1].
On days when the government issues a "Heatstroke Alert" (on TV and smartphone apps), avoid going outside or doing strenuous activity. The alert system is operated jointly by Japan's Ministry of the Environment and Japan Meteorological Agency[2].
Throughout summer, Japanese TV news, weather apps, and station signage display a number called WBGT (Wet Bulb Globe Temperature). It's not the air temperature — it is a composite index that combines temperature, humidity, and radiant heat into a single risk score. Because Japan's humidity matters as much as the heat, WBGT is a more honest measure of how dangerous the day actually is.
| WBGT ≥ 28 | Severe caution — stop strenuous outdoor activity |
| WBGT ≥ 31 | Danger — avoid all exercise |
| WBGT ≥ 33 | Heatstroke Alert issued |
| WBGT ≥ 35 | Heatstroke Special Alert (most dangerous) |
In 2025, Japan recorded 100,510 emergency transports for heatstroke — the highest annual total since data collection began in 2008. July alone accounted for ~40,000, followed by August (~32,000). The rate climbs sharply from June onward[6].
Source: Fire and Disaster Management Agency (FDMA), "Heatstroke Emergency Transport Report, May–September 2025"[6]. 57% of cases were people aged 65+. 38% occurred at home, 20% on the road.
The Japanese Association for Acute Medicine classifies heatstroke into three severity grades[3]. Tick the items that apply to you, a family member, or a colleague — the level of care needed will become clear.
→ Rest in a cool place and replace water and salt. If no improvement, suspect Grade II.
→ If the person can't drink water, or doesn't improve — see a doctor. IV fluids are often required.
→ Even one item below means you should call emergency services. Keep cooling the body while you wait.
Note: These checklists are a guide, not a diagnosis. If concerned, seek medical care early. For non-emergency medical advice in some areas of Japan, dial #7119 (limited regional service).
People who haven't acclimatized to heat yet (a 7–14 day process), those working outdoors for long hours, and those with weakened temperature regulation face the highest risk[4].
Direct sunlight plus physical exertion. Japan's revised Industrial Safety and Health Regulations (effective June 2025) require employers to monitor body condition and provide cooling facilities.
Returning to commuting after working from home, new hires, or staff reassigned to outdoor roles — none have acclimatized yet. Keep the first 1–2 weeks short, with extra breaks and hydration.
Reduced thirst response and weakened temperature regulation. Heatstroke can occur indoors. Use air conditioning and drink water on a schedule, not on thirst. ~57% of all emergency transports involve people aged 65 and over, and 38% of cases occur at home.
Heart, kidney, diabetic, or psychiatric conditions raise risk, particularly with medications that affect sweating or temperature control.
Your body can adapt to heat, but it takes time. Once acclimatized, you sweat more efficiently, your body cools itself better, and your heatstroke risk drops sharply — even at the same temperature. The process typically requires 7–14 days of repeated heat exposure[4].
⚠ A full day outdoors is a special case. Construction, delivery, agriculture, outdoor events — even an acclimatized body has limits during a long day in the sun. On days when WBGT exceeds 33 (Heatstroke Alert), plan work hours, breaks, and hydration in advance. Don't rely on willpower.
Untreated heatstroke can be rapidly fatal. If severe, call an ambulance and start cooling on the spot at the same time[4].
Free to call from anywhere in Japan.
A three-way interpretation service is available 24/7 in 15 languages, including English, Chinese, Korean, Thai, Spanish, French, Portuguese, Vietnamese, Indonesian, and more[5]. If you don't speak Japanese, simply say "English, please" and an interpreter will join the call.
Note: Ambulance service in Japan is free. There is no charge. Do not let cost worries delay your call.
When a worker or family member whose first language is not Japanese needs medical care — or when employers need help coordinating it — use these regularly updated public hotlines maintained by Japanese government agencies.
Provides information on Japan's medical system and refers to multilingual medical facilities. Languages include English, Chinese, Korean, Thai, Spanish, Portuguese, and more.
A 24/7 public hotline that can refer callers to English-speaking medical facilities and guide them through emergency procedures. Useful for after-hours or weekend situations.
Search Tokyo hospitals and clinics by supported language, specialty, and ward.
Note: Information current as of June 2026. Please verify hours and phone numbers on each organization's official site before calling.
Japan's revised Industrial Safety and Health Regulations (effective June 2025) require employers to put heatstroke prevention measures in place. WELD Consulting Group's occupational physicians and health professionals help companies design and operate those measures — including support for non-Japanese-speaking staff.
Contact us →Disclaimer: This page is public health information, not medical advice. In an emergency, dial 119. Treatment decisions should follow the instructions of a qualified physician. Information is current as of June 1, 2026 — please verify latest details on each official site.