# Cold water immersion looked very different across 11 studies and 3,177 healthy adults, with inflammation rising right away, stress easing 12 hours later and mood showing no reliable lift even as sleep quality and sickness absence hinted at narrower benefits

> Cold-water immersion keeps getting sold as a fast route to better mood, sharper focus and stronger health. A new review of randomized trials points to a more uneven picture. Across 11 studies involving 3,177 healthy adults, researchers found that inflammation rose soon...

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Byline: ARGO.net Editorial Team
Published: 2026-08-04T01:15:02+00:00
Categories: Health, News

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**Cold-water immersion** keeps getting sold as a fast route to better mood, sharper focus and stronger health. A new review of randomized trials points to a more uneven picture. Across **11 studies** involving **3,177 healthy adults**, researchers found that inflammation rose soon after exposure, stress dropped only 12 hours later and mood did not improve in a reliable way.

The [**review**](https://doi.org/10.1371/journal.pone.0317615), published in **PLOS ONE** on January 29, 2025, focused on cold showers, ice baths and cold plunges at 15 degrees Celsius or lower, with exposures lasting from 30 seconds to 2 hours. The authors limited the analysis to randomized studies in adults without chronic illness, which makes the result more useful than the usual mix of testimonials, athlete recovery studies and uncontrolled wellness claims.

Researchers from the University of South Australia said in a [public release](https://www.sciencedaily.com/releases/2025/01/250131110704.htm) that "the study reveals time-dependant and nuanced effects on health and wellbeing measures." The same intervention that produced a short-term inflammatory response also showed delayed stress relief, while several popular claims, especially around mood and immunity, stayed weak or inconsistent.

## What the review measured

**Tara Cain** and colleagues ran a **systematic review and meta-analysis** of trials published between 2014 and 2023. They screened ten databases, followed the [PRISMA 2020 statement](https://doi.org/10.1136/bmj.n71) and registered the protocol on PROSPERO before completing the analysis. Their inclusion rules were strict: adults had to be at least 18, the water had to be 15 degrees Celsius or colder, the immersion had to last at least 30 seconds and the water had to reach chest level or higher.

Most of the included interventions were baths rather than showers. Ten studies used tubs or similar immersion setups and one used cold showers. Water temperatures ranged from 7 to 15 degrees Celsius. Some studies looked at a single exposure, while others followed repeated sessions. The outcomes stretched across sleep, stress, fatigue, energy, immunity, inflammation, mental wellbeing, anxiety, depression, concentration, alertness, focus and quality of life.

The strongest pooled signal was an early rise in **inflammation**. The review reported a significant increase immediately after cold-water immersion and again one hour later. Stress moved in the opposite direction, though only after a delay: the pooled result showed a significant drop at 12 hours, while immediate, one-hour, 24-hour and 48-hour stress results were not significant. For readers used to simple promises about cold plunges, that timing detail is one of the most important findings in the paper.

## Why the stress result came later

Numbers alone do not explain why the results split across time. **Ben Singh**, one of the study authors, said the immediate response is a stress reaction: "The immediate spike in inflammation is the body's reaction to the cold as a stressor." The paper itself also describes cold exposure as something that activates the autonomic nervous system and changes hormonal and immune signals soon after immersion.

A person may therefore feel different later without showing an immediate pooled benefit in the first hour. A cold plunge pushes the body into a sharp response first. Heart rate and breathing can shift quickly. Inflammatory markers can also change. If any calming or recovery effect follows, it may arrive after that first wave rather than during it. The review leaves the full mechanism unresolved. Its time pattern challenges the idea that every benefit should appear right after the water feels coldest.

Earlier [sports-focused evidence](https://doi.org/10.1007/s40279-015-0431-7) already suggested that cold-water immersion can do different things depending on timing and context, especially when exercise is involved. The new review tried to move beyond that athlete-centered literature, yet some of the included trials still came after exercise or heat training. The delayed stress result may reflect cold exposure or recovery state, with study design also influencing the timing. It should not be read as a universal effect that would appear the same way in every healthy adult.

## How the 29 percent shower result fits

One of the most eye-catching findings in the paper did not come from the pooled meta-analysis at all. It came from a large [randomized cold shower trial](https://doi.org/10.1371/journal.pone.0161749) in 3,018 adults. Participants took 30, 60, or 90-second cold showers for 30 days and the study reported a 29 percent reduction in sickness absence compared with a control group.

**Buijze et al.** also found slightly higher **quality of life** scores after 30 days in the cold-shower groups. By 90 days, the quality-of-life difference had faded from statistical significance, which makes a lasting benefit harder to claim. The review authors were careful here. They noted that sickness absence was self-reported and that fewer missed workdays did not come with fewer total illness days. A person may have felt more able or more willing to work, but the study could not show that cold showers prevented illness itself.

Sleep sits in a similar category. The review points to better **sleep quality**, yet that result came from a single moderate-quality study in males after heat training. Mood is even thinner. Only one randomized study in the review measured mood directly and it found no significant difference. The clearest conclusion is simple: broad claims that cold water reliably improves **mood** are ahead of the evidence now available from randomized trials.

## Why the evidence is still narrow

The headline participant count looks large, but the evidence base is still small in the ways that matter most. One shower trial supplied 3,018 of the 3,177 participants. Only one included study enrolled women and that single study accounted for the female majority in the full sample. Outside that outlier, the remaining studies were made up entirely of men. A finding can look precise on paper and still apply to a narrow slice of the population.

Study quality was fair rather than definitive. The mean PEDro score was 6.4, with seven studies rated moderate quality and four rated high quality. Protocols also varied widely. Some participants sat in cold water for seconds, some for much longer and several studies measured people after exercise. The authors say this heterogeneity likely contributed to the mixed results. It also makes it harder to identify an optimal temperature, duration, or frequency for people who are interested in trying cold exposure.

The review's final message is cautious for good reason. It points to targeted possibilities, especially around delayed stress relief, sleep and short-term quality-of-life scores, yet it also flags short-term inflammatory increases and thin evidence for immunity or mood. The authors argue that larger and more diverse randomized trials are still needed, along with better long-term follow-up and closer study of dose-response patterns. Until then, cold-water immersion looks less like a proven wellness upgrade and more like an intervention with **time-dependent effects**, a narrow evidence base and several open questions that popular hype has moved past too quickly.