What are the common misunderstandings about "natsubate" (summer fatigue)?
This answer is a draft. It stays unpublished until legal review and source verification are complete.
"Natsubate" (夏バテ) is a word you will hear everywhere in a Japanese summer. It describes feeling drained by the heat, but it is not a medical term. Its neighbour, heatstroke (熱中症, netchūshō), does have a clear clinical classification — and in 2025 Japan recorded its highest ever number of ambulance call-outs for it.
The numbers and the classification
Between May and September 2025, 100,510 people were taken to hospital by ambulance for heatstroke — the first time the figure has passed 100,000 since the statistics began in 2008 (Fire and Disaster Management Agency). 57.1% were aged 65 or over, and the most common place of onset was the home (38.1%).
The 2024 clinical guideline classifies heatstroke into four grades.
| Grade | Symptoms | Response |
|---|---|---|
| Grade I (mild) | Dizziness, light-headedness on standing, heavy sweating, muscle pain or cramps. Consciousness normal | Cool the body in a cool place; take in fluids and salt |
| Grade II (moderate) | Headache, nausea, fatigue, reduced concentration and judgement | See a doctor |
| Grade III (severe) | Impaired consciousness, convulsions, liver or kidney dysfunction | Hospital admission |
| Grade IV (most severe) | Core body temperature of 40.0°C (104°F) or above with a reduced level of consciousness | Intensive care |
Many of the symptoms people are tempted to call "natsubate" overlap with Grade II.
[Verify] The ambulance figures are from the Fire and Disaster Management Agency; the classification is from the Japanese Association for Acute Medicine's "Heatstroke Clinical Practice Guideline 2024". Check the original documents before publication.
Misunderstanding 1｜Natsubate is caused by heat alone
The gap between air-conditioned rooms and the outdoors, disrupted sleep and an unbalanced diet are also generally described as factors. And "natsubate" itself has no definition.
Misunderstanding 2｜Cold food and drink will put you right
It may feel better for a moment, but that alone cannot be said to change your condition.
Misunderstanding 3｜If you have no appetite, you need not eat
Finding a form of food you can manage is recommended. Going on without eating is not desirable.
Misunderstanding 4｜Fluids alone are enough
When you have sweated heavily, public advice calls for attention to both fluids and salt.
Misunderstanding 5｜Sluggishness is just natsubate, so there is nothing to worry about
If you have any symptom at Grade II or above in the table — headache, nausea, poor judgement, no sweating, a rising body temperature — move to a cool place at once and see a doctor. Heatstroke can kill.
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Sources
- Fire and Disaster Management Agency (総務省消防庁), "Heatstroke information" [熱中症情報] (ambulance transport figures)
https://www.fdma.go.jp/disaster/heatstroke/
- Ministry of the Environment, Heat Illness Prevention Information site, "Heat Illness Environmental Health Manual" [熱中症環境保健マニュアル]
https://www.wbgt.env.go.jp/pdf/envman/full.pdf
- Ministry of Health, Labour and Welfare, information and materials for heatstroke prevention
https://www.mhlw.go.jp/seisakunitsuite/bunya/kenkou_iryou/kenkou/nettyuu/
⚠️ Editorial note: the source URLs above were identified by search. Our working environment cannot reach go.jp domains, so the contents have not been checked against the text. Verify every source before publication and record who checked it and when.
About this article
What we share here are ideas and everyday practices passed down among people living in Japan, together with general information drawn from public sources. They are not official recommendations, and they are not professional instruction. Practices vary between households and regions.
This is general information. Results vary from person to person and depend on your own conditions and surroundings.
Please decide for yourself, using your own judgement, whether any of this suits your situation. We cannot accept responsibility for any damage, loss or injury arising from following this article.
This article is not meant to diagnose or manage any specific medical condition. If you are worried about your health, see a doctor rather than relying on your own judgement.
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