Expert Column: Getting Used to the Heat — Easing into Summer 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 May column, written in late spring, when the first hot days arrive in Japan.

Preparing for summer before it arrives

Once mid-May has passed, there are days so warm in Japan that people find themselves saying, “Is it summer already?” In the traditional calendar of Eastern medicine, summer care is said to begin with Rikka, “the start of summer,” in early May. It is no exaggeration to say that how we look after ourselves now can shape how we feel in the height of summer.

Precisely because it is not yet full summer, now is the time to prepare the body to get used to the heat. This preparation is called shonetsu junka — heat acclimatization — and in recent years it has drawn attention in the medical field as well.

What is heat acclimatization?

Heat acclimatization is the process by which the body adapts to hot weather. It describes a state in which the sweat glands work actively, so that a small amount of sweat is enough to cool the body efficiently. You might picture it as a car engine whose cooling system has been tuned to work at its best.

If summer arrives before the body has had this chance to adjust, it is said that the body may find it harder to manage its temperature in the heat. On the other hand, the idea of yojo is not to force yourself into the heat, but to let the body get used to it slowly and gently.

A fermentation bath: practicing a gentle sweat while you relax

This is where I would like you to try a fermentation bath (enzyme bath). A fermentation bath uses the heat created as rice bran and wood chips ferment through the work of microbes. Although the material is quite hot, the warmth is thought to feel relatively soft on the body.

Many people describe the sensation as being “warmed slowly, right to the core,” different from an ordinary bath, and the warmth naturally invites a sweat. In other words, one of the great features of a fermentation bath is that you can practice sweating — the very thing heat acclimatization is about — while you relax.

Tips for making it part of your early-summer routine

• Once or twice a week, at an easy pace. There is no need to do it perfectly every day.
• Drink and rest afterwards. After the bath, have plenty of water and let your body rest. That, more than anything, is the heart of yojo.
• Make time to switch to “rest” mode. After bathing, try a little lavender aroma, or slowly enjoy a cup of lukewarm tea, and be aware of shifting to the parasympathetic nervous system — the body’s brake.

“Sweat, then settle.” This simple flow can be said to be the most natural way to help the body get ready for summer.

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.

Making friends with the heat

As the warm days of May continue, rather than putting it off with “It’s not summer yet, so I’m fine,” let the body gradually make friends with the heat through a fermentation bath. That is the most important first step toward a comfortable summer.

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.