Heat, Cold, and the Question Science Hasn’t Answered

A new review in Springer Nature’s International Journal of Biometeorology finds that nobody has proven the central pitch of contrast therapy, though it does not say the pitch is wrong.

Studios in Manhattan and Manly, Paris and Denver have spent the last eighteen months telling customers to sit in the heat, plunge in the cold and repeat, on the promise that the combination does something neither modality can do alone: a vascular pump, a nervous-system reset, recovery on a different timescale.

Heat and cold interventions: unveiling synergistic and counteractive mechanisms for health benefits, the narrative review published March 27 by Wafa Douzi, Erich Hohenauer, Benoit Dugué and colleagues, arrives as the contrast-therapy business runs ahead of the science. Studios are opening at a clip across three continents, and regulators are still figuring out how to classify them. Manufacturers are bundling saunas and cold plunges as integrated products. Consumers are paying premium prices on the assumption that hot-then-cold adds up to more than the sum of its parts.

The paper’s central claim is more cautious than any of that. “Although the effects of heat and cold exposures have been widely investigated,” the authors write in the abstract, “it remains uncertain whether combining these two stimuli offers greater, lesser, or simply different benefits compared with each modality alone. Relatively few studies directly compare these protocols.”

Who wrote it, and why their priors matter

The corresponding author, Wafa Douzi, is an associate professor at the MOVE laboratory at the University of Poitiers in France, a research group that has spent more than a decade studying how cold exposure affects autonomic, cardiovascular, and respiratory function in athletes and patients. Her doctorate, completed in 2018, was titled The Use of Cold in the Context of Recovery and Physical Exercise.

Her co-author Erich Hohenauer leads research at SUPSI in southern Switzerland and is the first author of the foundational 2015 PLOS One meta-analysis on post-exercise cryotherapy. Last year he was senior author of a randomized controlled trial in 30 women that found neither cold-water nor hot-water immersion accelerated recovery from exercise-induced muscle damage compared with a control group.

The senior author, Benoit Dugué, is a long-running cryostimulation researcher at MOVE and co-edited Springer’s 2024 reference book on whole-body cryostimulation.

None of these researchers are sauna industry voices. They are, if anything, sympathetic skeptics: scientists who have built careers on cold exposure and post-exercise recovery, and whose collective body of work has consistently found that the subjective benefits of these modalities (people feel better) tend to outpace the objective benefits (measurable physiological recovery markers move less reliably).

What the paper agrees with

The individual cases for heat and cold are not what is in question. The abstract is explicit: “Thermal strategies such as cold exposure and sauna bathing have been used for centuries to enhance recovery, with documented effects on improving cardiovascular health, reducing inflammation, and improving well-being.”

For sauna specifically, the evidence base is substantial. The Finnish Kuopio cohort under Jari Laukkanen has produced two decades of observational data linking frequent sauna use to lower cardiovascular and all-cause mortality. A separate January 2026 review in Quality in Sport described the cardiovascular mechanisms in detail, including improved endothelial function, lowered arterial stiffness, and blood-pressure reductions that compound with frequency. Cold exposure has its own well-mapped effects: a sympathetic surge followed by a parasympathetic rebound, brown-fat activation, anti-inflammatory signaling, and a documented improvement in subjective recovery markers like delayed-onset muscle soreness.

The new review challenges neither. It asks what happens when you put them together.

The combination question

The popular theory, repeated across studio websites, manufacturer marketing pages, and social-media protocol guides, is that heat and cold combine into a vascular pump. Sauna dilates blood vessels. The cold plunge constricts them. The rapid alternation, the theory goes, drives circulation, flushes metabolic waste, and trains the cardiovascular system in ways that single-modality exposure cannot.

The Douzi review treats this as a hypothesis, not a settled finding. The abstract notes that the paper “explores their individual and combined physiological mechanisms” and “examines how contrast therapy may induce synergistic benefits or potentially negate the effects of each modality.”

The two operative words there are may and or.

The surrounding 2024 to 2026 literature suggests that the combination adds benefit for some outcomes and none (or does harm) for others. A 2024 network meta-analysis in BMC Musculoskeletal Disorders found that contrast water therapy was the single most effective intervention for recovering creatine kinase, a marker of muscle damage. But for soreness and jump performance, cryotherapy alone outperformed it. A 2023 Sports Medicine review found that air cryotherapy beat cold-water immersion for muscular strength and immediate power, with both single-modality cold approaches generally outperforming contrast.

Contrast therapy is sometimes better than a single modality, sometimes equivalent and sometimes worse.

The counteractive question

The new paper also raises the possibility that the two modalities can interfere with each other. “The opposing physiological responses of each therapy may interfere with each other,” the authors write, “thereby compromising their effectiveness.”

The clearest case in the existing literature is muscle adaptation. A 2022 review in Sports Medicine - Open by Chaillou and colleagues, cited in the Douzi paper’s reference list, found that chronic post-exercise cooling, applied repeatedly across weeks, measurably blunts strength adaptations from resistance training. The cold reduces the inflammatory and reactive-oxygen signals that the body uses to remodel muscle. Used acutely after a single workout, this may not matter. Used as a daily habit by someone who lifts, it does.

The effect is documented, and it contradicts a piece of advice repeated in many contrast-therapy guides: cold immediately after sauna, immediately after lifting, every day.

Four marketing claims the evidence has not settled

Several confident claims in current contrast-therapy marketing are not settled science.

A studio operator who tells members these things is repeating common knowledge that has settled into the practice. The update this paper invites is one word: plausibly. The evidence stops short of proven.

What the review does not say

The paper does not say contrast therapy is useless. It does not tell people to stop. It does not contradict the established benefits of sauna alone or cold immersion alone. It is a narrative review, a synthesis of existing studies rather than new data, and its central conclusion is that direct comparative trials are scarce and that the field needs more rigorous research on which protocols work best for which outcomes.

New studio openings in Paris, Quebec, and Australia, integrated heat-and-cold product lines, and contrast-therapy memberships all rest on a combination the underlying research has not directly tested. The same business is part of a shift in which contrast-therapy studios are competing for evening hours against bars and restaurants as well as gyms.

What centuries of Finnish practice do that the labs do not measure

Contrast bathing is not new and was not invented in California. Finns have been alternating intense heat with cold-water immersion for centuries, frequently by cutting a hole in a frozen lake (the practice is called avantouinti) and dipping after a sauna session. Finland has roughly three million saunas serving five and a half million people, more saunas than cars, and active winter-swimming associations whose memberships run well into five figures.

The Kuopio cohort that produced the foundational sauna mortality data is drawn from a population in which post-sauna cold dipping is a normalized cultural practice. The outcomes that body of work measures are also different from what the recovery literature looks at: lower cardiovascular mortality, lower all-cause mortality, lower dementia incidence, and reduced risk of pneumonia, observed across two decades of follow-up, rather than creatine kinase or vertical jump.

If contrast bathing were physiologically counterproductive in a meaningful way, those signals would be very hard to explain.

That is not a refutation of the Douzi review. The Finnish data is observational, the Kuopio researchers themselves are careful about causal claims, and the cold-dip component cannot be cleanly separated from the sauna component or from the broader Finnish lifestyle. But it does suggest that the question the lab review asks, which is whether contrast therapy adds up to more than its parts on a recovery timescale, may not be the only question worth asking.

The mood story the recovery science does not capture

A 2000 paper in the European Journal of Applied Physiology by Šrámek and colleagues measured what cold-water immersion does to circulating catecholamines, the neurochemicals associated with arousal, focus, and drive. Noradrenaline rose by roughly 530 percent. Dopamine rose by roughly 250 percent. Both stayed high for an hour or more after the dip. Subsequent work, including studies popularized by the Danish researcher Susanna Søberg, has reproduced the basic finding.

That subjective shift, often described by practitioners as a clean and surprisingly long-lasting high, may be the part of the contrast experience that most reliably works. It is also the part that best explains why the ritual persists culturally, even when the muscle-soreness and jump-test data are mixed.

Finland has been ranked first in the World Happiness Report every year since 2018. That ranking is driven by many factors that have nothing to do with bathing: social trust, low corruption, generous public services, predictable institutions. No serious researcher would credit the lakes alone. But the Finnish lifestyle as a system, including the near-universal availability of saunas and the cultural habit of post-sauna cold dipping in winter, is at least adjacent to the mood-regulation effects that the cold-exposure literature documents at the level of individual neurochemistry.

None of this answers the combination question the new review raises. It does suggest, however, that the question itself may be slightly miscalibrated. If the recovery markers are mixed, the cardiovascular and longevity signals are strong, and the mood effects are real, the right framing is probably not “does contrast therapy add up to more than the sum of its parts?” but rather “more of what, and over what timescale?”

The Douzi review asks the lab question. The Finnish data answers a population question, accumulated over generations rather than weeks.

What to do with this if you are a reader

Three points, drawn from the review and the surrounding literature:

One. If the goal is the cardiovascular and longevity benefits associated with regular sauna use, the evidence for sauna alone is well-established. Adding a cold plunge is not necessary to achieve them.

Two. If the goal is athletic recovery, the evidence is mixed and depends on what you are recovering from. Subjective soreness reductions are well-supported. Objective performance recovery is less consistent. And if you are chronically lifting and chronically cold-plunging immediately after, you may be working against yourself.

Three. If the goal is the contrast experience itself, including the ritual, the alertness, and the feeling of having done something, the science neither confirms nor denies that you are getting a uniquely valuable physiological dividend on top of what each modality offers separately. You may simply be enjoying it, which is a reasonable thing to pay for.

One input to that more rigorous research is knowing what a real contrast session contains in the first place, which almost no study has recorded. A Bangor University group is trying to fill that in with an international survey of session structure and cooling practice, and it is currently short of US responses.