Hot, warm, cold: Roman baths were built around those three temperatures, and the hammam kept the heat. What the research supports, what it does not, and how to bring the sequence home.
Researched. With one scene Walked, in Bath, 1994.
Hot, warm, cold. Roman baths were built around those three temperatures, and a Roman bather's visit usually ended in cold water. The hammam kept the heat. The science is only now catching up with the sequence. It says less than the carousels on your phone, and more than you might expect.
In 1994 I stood above the Great Bath in Bath. Steam lifted off green water fed by a hot spring, into a pool the Romans lined with forty-five sheets of lead. I had no camera that day; cameras were not easy then. What stayed with me was the plan of the place, more than the water. Around the Great Bath were warm and hot rooms, and a round cold pool where, as the museum puts it, a bather could take "an invigorating plunge after treatments in the warm and hot rooms".
The Romans called those rooms the tepidarium (warm), the caldarium (hot) and the frigidarium (cold). The hammam grew out of the Roman bath, joined to the Islamic tradition of steam bathing. It kept the warm room and the hot room: ılıklık and sıcaklık in Turkish. It also kept a cool room, soğukluk, where bathers undress and rest. In many Ottoman baths that cool room was folded into the changing room, and the cold pool dropped away. The modern cold plunge puts the Roman frigidarium back.
This essay reads that sequence honestly: what the research supports, what it does not, and what it asks of the person lying on the warm marble.
Most of what you will read online about heat comes from one place: a cohort of 2,315 men aged 42 to 60 in eastern Finland, followed for a median of 20.7 years. The men who used a sauna four to seven times a week had 63 percent fewer sudden cardiac deaths than those who went once a week. They also had about half the risk of dying from cardiovascular disease, and 40 percent lower risk of dying from any cause. The researchers called this an association, not proof. It also belongs to one kind of bath: dry Finnish sauna, 79°C on average, in middle-aged men.
A hammam is a different room. One of the very few published studies of a traditional hammam session (Karagülle and colleagues, 2011) recorded conditions of 35–45°C at 100 percent humidity. Fifteen healthy volunteers took a session of about an hour: twenty to thirty minutes lying on the heated stone, a kese scrub, a foam massage and a lukewarm rinse. Their pain scores fell by more than half and they reported feeling more relaxed. Their heart rate and body temperature rose slightly. Their blood pressure did not change, and neither did the two blood markers the team measured. It was a small study with no control group, and it is most of the evidence there is for the hammam itself.
So the honest move is to borrow from studies of the nearest kind of bath, and to say so each time:
Then the cold. A 2025 review of eleven randomised trials, with 3,177 participants, found that cold-water immersion lowered stress, though twelve hours later rather than right away. The few studies that measured sleep and quality of life found improvements. In one of them, people who took a thirty-day cold-shower habit had 29 percent fewer sick days. Inflammation rose immediately after immersion and was still up an hour later. Ninety-five percent of the participants were men, so the evidence is early.
You may have seen that cold water raises dopamine by 250 percent. That figure comes from a laboratory study in which people sat in 14°C water for a full hour. A two-minute plunge is a different dose.
A well-run thermal house is a piece of hospitality engineering, and the part that matters most is rarely the hot room.
In Japan, where bathing is a daily habit, inquest records in one prefecture listed 2,689 bath-related deaths over fourteen years. Nine in ten were people aged 65 or older, and more than half happened in winter. Deaths rose as the weather turned cold, and the authors' main recommendation was a warning system on cold days. Japanese public-health advice usually blames "heat shock", the swing from a cold room into hot water. Some researchers argue that overheating in the bath itself matters more. Both answers point to the same design: a warm changing room, water that is not too hot, and not staying in too long.
A good bath house gets those details right. Its entry and changing rooms are warm. It has water within reach, and an attendant who notices when someone has stayed too long. It does not serve alcohol near the heat. When I read a thermal hotel, these are the things I check, before the marble or the treatment menu.
The order of heat and cold matters too. One study (Owen and colleagues, Experimental Physiology) found that adding cold dips to the breaks between sauna rounds blunted the body's response to the heat. If you want what the heat does, keep the cold short, or save it for the end, as the Romans did.
The research points to a simple shape: heat, a short rest, cold, repeated two or three times. Ten to fifteen minutes of heat per round is close to the session lengths in the studies above. The part you finish on depends on the hour.
At home, the practice is smaller and easier to keep: a warm bath an hour or two before sleep, a cool rinse on waking, and a bathroom that is warm before you step out. On an Ontario winter night, that last one matters most.
The hammam study by Mine Karagülle and her colleagues ends in an unusually candid place. Their volunteers reported less pain and felt more relaxed, yet neither blood marker the team measured moved. So the authors did not claim a hidden molecule. They pointed to the session itself: heat, humidity, the kese scrub, the foam and the poured water, a run of stimuli on the skin that can quiet the signal of pain. I trust a study more when its authors admit their instruments did not find what they looked for.
That is the honest reading of the bath. It is not medicine, and it is not magic. It is a well-ordered sequence of rooms that the Romans designed and the hammam carried on. The place teaches the habit, and you carry the habit home.
For the reader's version — what to ask a thermal hotel before you book, and how to bring the sequence home — see Heat and Cold, Read Honestly on Orophile Journeys.
Educational reading, not medical advice.