We read the pushback on cold plunges. We agree with most of it.

Brass Monkey response to "Science is pushing back on the hype over cold plunges", National Geographic, 13 July 2026.

This month, National Geographic published this careful piece arguing that the science on cold-water immersion has not kept pace with the hype. Celebrities swear by it, influencers credit it with everything from fat loss to longevity, and a growing number of researchers are, rightly, throwing some cold water on those claims.

Here is our position, plainly: they are right, and we are glad someone with that reach said so.

The claims the piece dismantles are the same ones we refuse to make. Below is what we say instead, what each position rests on, and the three places where we would correct the record. Including one where the article is more generous to cold water than we are.

Recovery and muscle growth

If you climb into cold water immediately after resistance training, you can compromise the adaptation you trained for. This is the best-supported caution in the entire field, and we have consistently said so.

It is also more specific than it is usually reported, and the specifics matter commercially.

A systematic review and meta-analysis found that cold-water immersion immediately after resistance exercise attenuates hypertrophic gains compared with no immersion (Piñero et al., 2024). Earlier controlled work showed the same direction for muscle mass and strength, alongside blunted acute anabolic signalling (Roberts et al., 2015; Fyfe et al., 2019).

But the meta-analysis on strength outcomes splits the result in a way that is rarely quoted. Overall, immersion attenuated strength gains (effect size −0.23). In the studies that cooled only the trained limb, the effect held (−0.31). In studies using whole-body immersion, it did not: effect size = −0.08, not statistically significant (Grgic, 2022).

The mechanistic work points in the same direction. The study showing reduced muscle microvascular perfusion and lower incorporation of ingested amino acids into muscle protein used a single-leg design, with one leg in 8°C water and the other in thermoneutral water as its own control (Betz et al., 2025). It is elegant and not a cold plunge.

So the honest reading is this. Cooling a muscle you have just trained interferes with its rebuilding, and the mechanism is well described. Whether whole-body immersion, at a normal dose, in the way people actually use it, carries the same penalty is genuinely less certain than the headlines suggest.

That uncertainty is not a licence. Our guidance is unchanged: do not put cold immediately after hypertrophy work as a matter of routine. Timing and purpose decide whether cold helps or hinders (Ihsan et al., 2021). But we are not going to overstate the evidence against ourselves any more than we would overstate it in our favour.

Metabolism and weight loss

Cold does activate brown adipose tissue. That was established in the landmark 2009 imaging work that arguably started the modern movement (van Marken Lichtenbelt et al., 2009; Cypess et al., 2009). It does not follow that plunging melts fat off you. The additional energy expenditure during a brief immersion is small, and it is not the basis of a weight-loss strategy.

The metabolic evidence that does look interesting comes from a different intervention entirely: longer, milder cold acclimation, not brief plunges. Ten days of mild cold acclimation improved peripheral insulin sensitivity in people with type 2 diabetes (Hanssen et al., 2015). A later trial using a milder protocol found no such improvement (Remie et al., 2021). Two well-conducted studies, opposite results, different protocols. That is the honest state of the field, and it is why we describe metabolic effects as protocol-dependent and use "may" rather than "will".

Anyone extrapolating from acclimation studies to a two-minute plunge is changing the intervention and keeping the conclusion.

Testosterone, libido and longevity

On testosterone and libido, there is no reliable human evidence of a durable increase, and at least one recent review raises the possibility of a decrease. We therefore make no claim in either direction.

On longevity, there is no long-term outcome data in humans. Every claim about lifespan is an extrapolation from acute or short-term physiological studies in small samples. We make no longevity claims, and we would treat anyone who does with suspicion.

The risks

This is the part the hype tends to bury, and the part we take most seriously.

The initial cold shock response is a genuine cardiovascular stressor: a sharp inspiratory gasp, hyperventilation, tachycardia and a rise in blood pressure. It is well characterised, which is why cold water can be dangerous rather than merely unpleasant (Tipton et al., 2017). Simultaneous activation of sympathetic and parasympathetic drive during immersion has been proposed as a mechanism for arrhythmia in vulnerable individuals (Shattock and Tipton, 2012). Cold exposure also carries specific cardiovascular considerations for people with existing disease (Ikäheimo, 2018).

Most healthy people tolerate these shifts. Some people should not enter cold water without medical clearance. Screening, contraindications, coached entry, never plunging alone, protecting the hands and feet, and controlled rewarming are not optional extras bolted on for insurance. They are the practice.

One point of terminology, because it changes what you watch for. The repetitive-immersion injury described in commercial fishermen, and the risk to hands and feet generally, is non-freezing cold injury. It is a distinct pathology from frostbite, which requires tissue to freeze and therefore does not occur in liquid water above 0 °C. The distinction matters operationally: non-freezing cold injury develops slowly, over repeated exposures, and presents as persistent numbness, pain, and sensory changes rather than as an acute emergency. It is a reason to protect extremities and to avoid excessive frequency, not a reason to watch for blackened fingers.

Three places we would correct the record

We’re not interested in defending cold water against this article. We’re interested in the claims being right in both directions, so here are the places we would push back, including one where the piece is too kind to us.

One: frequency. The article closes on the advice that plunging more than once a week is usually unnecessary. We think this is the weakest recommendation in the piece, and possibly the least safe.

The adaptation with the strongest evidence and, by far, the most safety-relevant is habituation of the cold shock response. That gasp-and-hyperventilate reflex is what drowns people, and it can be substantially blunted with repeated exposure (Barwood et al., 2024). Habituation is driven by repeated, closely spaced exposures, and it can be developed with something as low-risk as cold showers (Eglin and Tipton, 2004; Yurkevicius et al., 2021). It also decays if not maintained (Tipton, Mekjavic and Eglin, 2000).

Weekly frequency sits at or below the floor for developing the response that keeps people safe. Our own progression is deliberately the other way round: frequent, brief, mild exposures first, with immersion introduced sparingly and later.

This produces a position we suspect will surprise people. We are arguing for more frequent and much milder cold exposure than the article recommends, on safety grounds, not for less.

Two: the temperature floor. The suggestion that there is no point in going below 10°C, because colder water produces no additional measurable benefit, is stated more firmly than the evidence supports. Physiological responses to immersion are graded by temperature, not flat below a threshold (Šrámek et al., 2000), and recovery outcomes vary by both temperature and duration in ways that differ across outcomes (Machado et al., 2016; Wang et al., 2025).

That is not an argument for colder. It is an argument that "colder does nothing extra" and "colder is not better for you" are different statements, and only the second one is safe to make.

Three: sleep, where the article is more generous than we are. The piece suggests immersion may improve sleep, partly because a fall in core temperature is a natural sleep signal. We hold sleep effects at a lower confidence than that. The reasoning conflates the thermal change produced by immersion with the circadian decline in core temperature, and post-exercise immersion can produce a delayed, rather than a clean, further fall in core temperature. Effects on sleep appear real for some people and are state- and timing-dependent. We say "may", and we say it about a subset of users.

We include this one deliberately. A brand that only corrects the criticisms is not auditing its claims; it is defending its product.

Where we would sharpen the question

The article mostly asks, "Does cold water work?" We think that framing is what created the mess in the first place.

Cold water is not a pill with a single effect you can prove or debunk. It is a controllable stressor, and whether it helps or harms depends on the dose, the person, their state and their purpose. Dose is not one number. It is temperature, duration, frequency, immersion depth, and the context it sits in. Change the paradigm from one limb to whole body, or from a plunge to ten days of mild acclimation, and the answer changes with it. That is not the evidence being weak. That is the evidence being specific.

The wider base on health and wellbeing remains mixed enough that confident universal claims are not supportable in any direction (Espeland et al., 2022; Cain et al., 2025). We think that is the correct place to be, and we would rather say so than pick whichever studies flatter us.

That is why we do not prescribe cold by temperature and a stopwatch. We prescribe the minimum effective dose for the right person, in the right state, for the right purpose. What that trains is not a bigger promise. It is Readiness: not protection from stress, but the capacity to meet it.

The researchers quoted in the piece converged on a summary we nearly agree with: not that cold, not that long, not that often. We would keep the first two and query the third. Colder and longer are not better, because cold is a stress, and the aim is a calibrated adaptive response rather than the largest dose you can survive. But not that often, applied to the exposures that build habituation, gets the safety argument backwards.

The honest version of cold water is less dramatic than the internet would like. Fewer miracles, more judgment. That is the version we build, and it is the only one worth doing.