If you want to get the most out of heat therapy, newer science points to a surprising answer: immersion in hot water raises core body temperature the most of all — and was the only method in the study to trigger a measurable immune response. That doesn’t mean sauna is worse; each method works a little differently. The comparison below is based on new research by physiologists at the University of Oregon and will help you choose based on what you actually want from wellness at home.
What exactly did the new study find?
In June 2025, researchers at the Bowerman Sports Science Center at the University of Oregon published a study in the American Journal of Physiology. Led by physiology professor Christopher Minson and doctoral researcher Jessica Atencio, the team directly compared three ways of heating the body: hot water immersion (hot tub), the classic Finnish dry-heat sauna, and the more modern infrared sauna.
Twenty healthy, regularly active volunteers took part — 10 men and 10 women aged 20 to 28. Before, during, and after each session, the team measured several indicators: core body temperature, blood pressure, heart rate, cardiac output, immune cell populations, and inflammatory markers in the blood.
The key finding is simple. Hot water immersion raised core body temperature the most. The reason is physical: in water, the body cannot dissipate heat through sweating or radiation into the air as effectively as in a sauna. “A rise in core temperature is the main trigger for the downstream responses,” explains Atencio. And because core temperature is the deciding factor, the hot tub proved to be the most effective stimulus by this measure.
Why does core temperature matter so much?
When internal temperature rises, blood flow increases too. “A rise in body temperature leads to greater blood flow, and the sheer force of blood moving against the vessel walls is beneficial on its own,” says Atencio. According to the study, all three methods increased blood flow — good news for your vessels no matter which one you choose.
The difference showed up in immunity and inflammation. Only the hot bath triggered an inflammatory response, measurable through inflammatory cytokine levels and changes in immune cell populations. This isn’t inflammation in the sense of illness; it’s a short-term, controlled stress stimulus that the body responds to by adapting — much like it does to exercise.
The authors remain cautious, and this article deserves the same caution. The subjects were young, healthy, trained individuals, so the results can’t automatically be applied to older adults or people with chronic conditions. And as Minson stresses, heat therapy works best as a supplement, not a replacement, for exercise: “If you repeat these stimuli over time, our lab and many others have shown they’re associated with better health.”
It’s worth highlighting what the study did not measure. It didn’t look at weight loss, sleep quality, or relief from specific conditions, and it doesn’t claim that heat “cures” anything. It examined the body’s acute physiological response — temperature, circulation, and immune markers — to a single session and their short-term course. The authors base the long-term benefits on repeated exposure and on findings from earlier research, not on a single measurement. That’s exactly why it makes sense to see the hot tub and the sauna as part of a healthy lifestyle, not as a miracle switch.
Hot tub vs. Finnish sauna vs. infrared sauna: comparison table
The study compared physiological effects. In practice, though, operating temperature, space, cost, and year-round usability matter too. The overview below combines the study’s findings with commonly cited operating parameters for each technology.
| Parameter | Hot tub (hot water bath) | Finnish sauna (dry heat) | Infrared sauna |
|---|---|---|---|
| Typical environment temperature | 34–40 °C (water) | 70–100 °C (air) | 45–60 °C (air) |
| Heating mechanism | Heat conduction through water; the body can’t cool by sweating | Heated air and radiant heat from the stove | Infrared radiation heats the body directly |
| Effect on core temperature (per the study) | Highest increase | Moderate | Mildest |
| Immune/inflammatory response (per the study) | Only method with a measurable response | No measurable response | No measurable response |
| Blood flow / circulation | Increased | Increased | Increased |
| Space and installation | Deck, garden, or indoors; needs load capacity and a water supply | Dedicated room, wooden cabin, ventilation | Compact cabin, just needs a standard 230 V outlet |
| Operating costs | Higher (constant water heating, chemicals, filtration) | Higher stove output, but short sessions | Lower power draw, quick heat-up |
| Year-round use | Yes, even outdoors in winter | Yes | Yes |
| Social dimension | High — more people, longer sessions | Moderate | Lower — usually 1–2 people |
Hot tub water temperatures typically range from 34–40 °C, and for both hygiene and comfort it’s generally recommended not to exceed around 40 °C. Finnish saunas operate at significantly higher air temperatures but with lower humidity and shorter session times. Infrared saunas rely on a lower air temperature and heat the body directly through radiation, which many find easier to tolerate.
Who is each one suited for?
Recovery after sport
The study looked at regularly active individuals, and all three methods increased blood flow, which is key for recovery. The hot tub also has the advantage of buoyancy in water and the ability to direct jets at strained muscle groups. Infrared saunas tend to be the choice for those who tolerate the high heat of a Finnish sauna poorly and want a longer, milder warm-up.
Sleep and relaxation
Many people subjectively associate warming the body followed by gradual cooling with falling asleep more easily. The Oregon study did not directly measure this specific factor, so treat it as a widely recognized comfort effect of heat, not as one of its conclusions. Both hot tub and sauna work well here — it comes down more to personal preference and what actually helps you unwind in the evening.
Back pain and stiffness
Heat increases blood flow to tissue, and many people find it soothing for stiff muscles. The hot tub adds hydrostatic buoyancy, which takes pressure off the spine and joints, making it popular with people who have sensitive backs. This isn’t a treatment — for persistent or severe pain, a doctor should always have the first word.
Cardiovascular health
According to the study, heating the body increases blood flow, and repeated heat exposure may, over time, help lower blood pressure and improve the body’s response to heat stress. The authors explicitly frame this as supporting a healthy lifestyle, not as a replacement for exercise. In their view, regular physical activity brings comparable or greater benefits; heat is a complement.
Safety: when to be careful and when to consult a doctor
Heat therapy is safe for most healthy people when used in moderation. Still, there are situations that call for caution and professional advice.
- Pregnancy: raising core body temperature, especially in hot water, is a sensitive issue during pregnancy. Consult your doctor or gynecologist before using a hot tub or sauna.
- Heart and vascular conditions: heat changes heart rate, cardiac output, and blood pressure. People with heart disease, a history of heart attack, or unmanaged blood pressure should discuss heat therapy with a cardiologist.
- Medication and alcohol: some medications affect thermoregulation and blood pressure; alcohol in a hot tub further increases the risk of dehydration and fainting.
- Moderation and hydration: the study’s authors, and common practice, recommend short sessions, plenty of fluids, and never heating the body to the point of feeling unwell.
The authors themselves stress that heat therapy should be used “in moderation” and ideally after consulting a doctor. This rule applies doubly if you belong to any of the groups listed above.
The best solution? A combination of both
The study doesn’t pit the hot tub and the sauna against each other as winner and loser. It shows that they complement each other physiologically: the hot tub raises core temperature the most and was the only one to trigger an immune response, while all three methods boosted blood flow. Home wellness doesn’t have to be an either/or choice.
Many households combine an infrared sauna for quick, gentle warm-ups on weekdays with a hot tub for longer weekend recovery and time together. The hot tub also works year-round, even outdoors — in winter, warming up in the steam over a snow-covered garden is an experience in itself. If space is a concern, an infrared sauna fits into a smaller interior and needs only a standard outlet, while a hot tub needs a solid base and a water supply.
It helps to work through some practical questions before buying. How many people will use the wellness setup, and how often? Do you have outdoor space with sufficient load capacity, or are you looking for a compact indoor solution? How do you feel about running costs and maintenance — a hot tub needs regular water care, while a sauna needs ventilation and wood upkeep? The answers to these questions usually settle the decision before physiology does.
Whichever you choose, regularity and moderation are what matter most — it’s the repeated, sensibly dosed stimulus that scientists link to long-term benefit.
Frequently asked questions
Is a hot tub healthier than a sauna?
According to the University of Oregon study (2025), the hot bath raised core body temperature the most and was the only method to trigger a measurable immune response. That doesn’t mean sauna is “unhealthy” — all three methods increased blood flow. The hot tub was the strongest stimulus in this particular measurement, but your choice should also depend on space, cost, and your own preferences.
How long and how often should you use a hot tub or sauna?
The study doesn’t specify an exact session length, and there’s no universal formula. The authors recommend moderation and regularity — short sessions repeated over time, with plenty of fluids, and never heating the body to the point of feeling unwell. For a specific plan, especially with health conditions, follow your doctor’s advice.
What is the ideal water temperature for a hot tub?
The comfortable and hygienically recommended range is roughly 34–40 °C, with 40 °C generally cited as the upper limit for regular use. Higher temperatures put more strain on circulation and increase the risk of overheating for sensitive groups.
Can a pregnant woman or someone with heart disease use a hot tub or sauna?
Both groups should always discuss heat therapy with a doctor first. Rising core temperature and blood pressure changes are sensitive, individual issues in both pregnancy and heart disease — the general guidance in this article does not replace professional advice.
Is it worth having both a hot tub and a sauna at home?
If space and budget allow, combining the two makes sense, since the methods complement each other: an infrared sauna for quick weekday warm-ups, a hot tub for longer recovery and time together. Many households choose both rather than one instead of the other.
If you’re planning your home wellness setup, take a look at our range of hot tubs — from compact deck models to more spacious swim spas. For more tips on care and operation, see our Advice articles, where we also cover routine maintenance and troubleshooting.
