Expert Column: Summer Fatigue Comes from Chill, Not Just Heat — Warming Up with a Fermentation Bath

By Prof. Kazunori Ito
Professor, Faculty of Acupuncture and Moxibustion, Meiji University of Integrative Medicine / Director, Japan Enzyme Bath Association

Every month, Hakkou Ningen and Prof. Kazunori Ito publish a column on the enzyme bath — also called a fermentation bath — from the perspective of Eastern medicine and yojo, the Japanese tradition of everyday self-care. This is the English version of the August column, written for the height of Japan’s summer.

Summer fatigue: not “losing to the heat,” but “losing to the chill”

We tend to think of summer fatigue as simply being worn out by the heat. But that is not the whole story. Today, much of it may come from a chill that builds up deep inside the body — from air-conditioned rooms, cold drinks and long hours in light clothing.

With scorching heat outside and cool air indoors, the body is constantly asked to adjust its temperature. In car terms, it is like keeping your foot on the accelerator — the sympathetic nervous system, the body’s “go” mode — while the brake, the parasympathetic nervous system or “rest” mode, never gets a chance to work. The engine is overheating. Feeling heavy, having less appetite, staying tired even after sleep: Eastern medicine sees these vague signals as mibyo, a state that is not illness, but not quite full health either.

Warming slowly, from the inside

This is where we suggest a fermentation bath (enzyme bath). It uses the heat created as rice bran and sawdust ferment through the work of microbes, and it wraps the body in warmth without any hot water. Its special quality is that the warmth reaches slowly and deeply.

In Eastern medicine, warming the body from the core is thought to open up circulation and to help release the heaviness that builds up over air-conditioned days. At the same time, a gently warmed body naturally relaxes, and it is thought to shift more easily from the accelerator to the brake. Rather than adding something new in summer, you subtract the chill and tension you have been holding on to. That is the idea behind summer yojo.

Gently, and only as far as feels good

• Drink before and after. Have water regularly before and after the bath.
• Comfortable is enough. Stop while it still feels pleasant. Sweating more does not mean better.
• Any pace works. Once a week or once a month is perfectly fine.
• At home, too. On days when you can’t go out, simply soaking in a lukewarm bath at 38–40°C (100–104°F) one to two hours before bed is self-care in the same spirit.
• End the day gently. A cup of plain warm water after bathing, and going to bed by 11 p.m. if you can, is even better.

If you have a medical condition, or on days when you don’t feel well, please don’t push yourself, and talk to your doctor first.

Do what you can, when you can

There is no need to blame yourself on days when you can’t keep it up. Resting well on a tired day is also a fine form of yojo. Rather than aiming for perfection, do what you can, when you can. Little by little, bring back time in your daily life to warm and loosen your body — that is the gentlest way to feel like yourself again after a long, hot summer. This summer, why not make some time to get warm and cozy?

This column shares general ideas from Eastern medicine and the Japanese tradition of yojo. It is not medical advice, and experiences vary from person to person. The original column was written in Japanese for the Japan Enzyme Bath Association.

About Prof. Kazunori Ito

Prof. Ito is a professor in the Faculty of Acupuncture and Moxibustion at Meiji University of Integrative Medicine in Nantan, Kyoto, and a director of the Japan Enzyme Bath Association. He has spent many years in research and education in Eastern medicine, and works with Hakkou Ningen on joint research into the enzyme bath and on academic conference presentations.

Bringing the enzyme bath to your country

Guests come back to the enzyme bath for the experience itself: deep, enveloping warmth that comes only from fermentation, the scent of wood and rice bran, and a one-to-one welcome from staff. At our own shops in Japan, around 90% of guests return — yet outside Japan, an authentic enzyme bath is still rare.

It is also a business that cannot be started just by buying tubs and materials. The heat comes from living microbes, and fermentation shifts with the climate, the building, the materials and the season. When it is not managed well, the bath will not warm up, odors appear and guests stop coming. That is why learning from people who actually run enzyme baths matters.

Hakkou Ningen has supported more than 80 enzyme bath openings across Japan — from snowy Hokkaido to subtropical Okinawa — and we are now preparing our first overseas shop in Los Angeles. You train hands-on for 7 days in a working shop in Miyama, Kyoto, and we can help you set up fermentation in your own climate, with materials shipped from Japan (where quarantine rules allow) or sourced locally. Our baths are known for their low odor — we have installed them in hotels, salons and even apartment rooms, and none of the shops we have supported has had to close because of odor. It is not a franchise: you open under your own name. And through our work with Prof. Ito, we keep studying the enzyme bath together with a Japanese university.

Thinking about offering an enzyme bath in your country? Message us on WhatsApp to get our free program guide — pricing, a business simulation and the full training curriculum — or visit our opening program page.