What are the common misunderstandings about bedroom temperature?

This answer is a draft. It stays unpublished until legal review and source verification are complete.

Sleep with the air conditioner on, or off? Opinions divide around the world, and Japan's humid summers make the question pressing for anyone newly arrived. Japan's official guidance gives actual numbers.

The numbers in the guidance

• Sleep Guide for Health Promotion 2023 [健康づくりのための睡眠ガイド2023] (Ministry of Health, Labour and Welfare, MHLW): a room temperature of 13–29°C during sleep is described as desirable, and 26–28°C in summer is reported to make sleep easier.
• Ministry of the Environment heatstroke prevention information: the often-quoted "28°C" — a figure you will hear everywhere in Japan in summer — is described as a guide for room temperature, not the air conditioner's set temperature itself.

[Verify] The figures above were confirmed through secondary sources. Before publication, check the original text of the Sleep Guide 2023 and the Ministry of the Environment heatstroke prevention information site.

Misunderstanding 1｜Air conditioning is bad for you even on hot days

Heatstroke happens indoors too. The Ministry of the Environment and the MHLW have repeatedly stressed the importance of managing room temperature, including while you sleep. Enduring the heat is the more dangerous choice.

Misunderstanding 2｜Setting the air conditioner to 28°C is enough

The set temperature and the room temperature are different things. Depending on insulation and sunlight, the room can pass 29°C even with the unit set to 28°C. Check the room with a thermometer.

Misunderstanding 3｜Lower the temperature and you will sleep

When humidity is high, sweat evaporates poorly, and the same temperature feels more oppressive. Aim for around 60% humidity, and watch temperature and humidity together.

Misunderstanding 4｜Air blowing directly on you is fine

A constant stream of air on the body can chill you. Simply pointing the airflow away from your body changes how it feels.

Misunderstanding 5｜In winter, the warmer the better

The lower limit in the guidance is 13°C. A bedroom that is too cold is not desirable, but heating dries the air, which can affect throat and skin. Think about warmth and dryness at the same time.

Misunderstanding 6｜One setting suits the whole family

Comfort varies with age and build. Even in a shared room, adjusting individually with bedding is more realistic.

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Sources

• Ministry of Health, Labour and Welfare, *Sleep Guide for Health Promotion 2023* [健康づくりのための睡眠ガイド2023] (adopted February 2024)

https://www.mhlw.go.jp/stf/seisakunitsuite/bunya/kenkou_iryou/kenkou/suimin/index.html

• Ministry of the Environment, Heat Illness Prevention Information site [熱中症予防情報サイト]

https://www.wbgt.env.go.jp/

• Ministry of Health, Labour and Welfare, heatstroke prevention information and materials site [熱中症予防のための情報・資料サイト]

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.

Sources

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