Making Waves in Cold‐Water Immersion/Swimming Research: Towards a Balanced Assessment of Therapeutic Efficacy and Water Safety

Open water swimming, including cold-water immersion, has grown increasingly popular in the United Kingdom; since 2016 there has been a 138% increase in people reporting to open water swim at least twice a month [1], partly observed by a rise in interest in organised events for open water swimming and by the purported health benefits of cold-water immersion [2]. Yet these benefits are often based on case studies [3], including a growing literature of peoples’ experiences [4], and require thorough investigation of their efficacy and underlying mechanisms. This gap in knowledge highlights the need for rigorously designed studies to substantiate therapeutic claims, weigh up the balance against the risks and to elucidate the mechanisms involved. Although the focus on cold-water immersion for these studies is the potential for therapeutic effect, it is necessary to identify that cold-water immersion is hazardous, and omission of potentially fatal consequences paints an inaccurate picture of the relative efficacy of the intervention. In the United Kingdom, approximately 200–300 accidental water-related deaths occur annually, and in 2024 alone, 22 people died while outdoor swimming (gross unadjusted number) [5]. Therefore, research in this field must also address the associated risks, particularly the cold shock response [6]. The CSR occurs in the initial moments of immersion, resulting in rapid skin cooling that activates cutaneous cold receptors and provokes an autonomic sympathetic response marked by a sudden inspiratory gasp (approximately 2.4 L in 15°C water) followed by uncontrolled hyperventilation. This impairs breath-holding ability and elevates drowning risk in open water, though controlled, incremental or partial exposures (e.g., cold showers) may pose less danger. Concurrent intense peripheral vasoconstriction and tachycardia increase cardiac workload, potentially precipitating adverse cardiovascular or cerebrovascular events—risks that can be exacerbated by arrhythmias during cold-water immersion with disease, breath-holding or facial submersion [7-9]. Crucially, before evaluating potential therapeutic benefits, comprehensive safety protocols must be established, incorporated into the research design and clearly communicated at all points, especially when disseminating the findings. There are also other complications that can occur that have fatal or long-lasting consequences if not recognised, mitigated and dealt with if they occur, such as physical incapacitation, hypothermia, rewarming collapse, non-freezing cold injuries [10], swimming-induced pulmonary oedema [11], cold urticaria [12] and transient global amnesia [10, 11]. To mitigate these hazards, laboratory investigations routinely implement rigorous participant screening. However, screening cannot eliminate risk entirely, as evidenced by fatalities among fit, medically cleared athletes during the swim phase of triathlons [13] or the occurrence of transient global amnesia during a laboratory research study [14]. Thus, the very mechanisms thought to be beneficial may prove hazardous for some individuals. Although the risks are applicable to all cold-water environments, open water settings demand particular caution due to additional natural and manmade hazards, including but not limited to waves, currents, tides, unstable banks, fast-moving water and submerged objects as well as pollution and pathogens from poor disposal practices, land run-off and spills. Consequently, any investigation of the potential benefits of cold-water immersion requires development of comprehensive and robust risk-mitigation measures as well as the data collection processes. Table 1 presents recommended precautions for cold-water immersion research in accordance with Tipton et al. [15]; this table is not exhaustive, and mitigation protocols should be adapted to the specific context and individual study circumstances. Furthermore, Tipton et al. [15] identify medical conditions for which cold-water immersion is contraindicated. Also of note, individuals may be unaware of underlying health conditions [16]; therefore, anyone experiencing ill health should be encouraged to seek medical evaluation prior to cold-water exposure. These medical exclusions underscore the necessity of understanding the mechanisms and causal factors underlying any observed changes in interventional studies of cold-water immersion. For individuals for whom cold-water immersion in any form is contraindicated, alternative activities with analogous properties may be considered; however, identifying these ‘active ingredients’ depends on comprehensive data collection during trials. It is therefore relevant to precisely document all immersion and swimming procedures, because numerous contextual factors, such as participation in a research study, heightened engagement from the research team, peer support, exposure to natural environments or increased physical activity, may influence patient-reported outcomes independently of cold-water exposure. Table 2 offers a checklist of reporting items for manuscripts. Although these measures may not yield conclusive findings on their own, they are essential for advancing the research field, providing data for future meta-analyses and promoting safe activity. In summary, to offer a balanced assessment of the efficacy of cold-water immersion or swimming interventions, peer-reviewed manuscripts must clearly disclose both potential harms and benefits, the safety mitigations in place and, based on the evidence gathered, outline any mechanisms of action. The authors have nothing to report. Data sharing is not applicable to this article as no datasets were generated or analysed during the current study.