Question & Answer

Does cold sea-water swimming improve general health, mental health and the immune system?

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  • Open-water swimming is a popular sport that grew in many parts of the world during the COVID-19 pandemic and restrictions on indoor sports.
  • Cold-water swimming enthusiasts claim that it can improve general health, mental health, and the immune system.
  • In January 2023, claims circulated in social and mainstream media warning open-water swimmers about the risks of swimming-induced pulmonary oedema, a dangerous condition that causes fluid in the lungs. This was based on findings from a single case report published in a medical journal.
  • Case reports often describe the experience of just one person, and tend to focus on patients who have rare or unusual  symptoms.
  • It has also been suggested that exposure to intensive short-term, cold stimuli such as swimming in cold water is a possible form of body hardening. Hardening means exposure to a natural stimulus, resulting in the body being better able to resist  stress and diseases.
  • In a number of studies (Study 1, Study 4, Study 5, Study 6, Study 7, Study 8, Study 9, Study 10), blood samples were taken from groups of people who regularly took part in cold-water swimming. To test for any differences these samples were compared to either before and after the cold-water swimming season, (Study 5, Study 7, Study 9) or to the blood samples of non-swimming groups (Study 1, Study 4, Study 6, Study 8, Study 10).
  • Some of these studies (Study 6, Study 7, Study 8, Study 9, Study 10) used the blood samples to examine the impact of cold-water swimming on hormones in the blood, like adrenaline, noradrenaline, and cortisol. These are known as “stress hormones” because they are released in response to stressful situations. Most of these studies found that cold-water swimming had a positive impact on the regulation of these hormones, except for Study 8, which did not report any significant effects.
  • Some studies (Study 1, Study 4, Study 5) used the blood samples to examine important components of the body’s defence system that are present in the blood, such as red blood cells, white blood cells or platelets. The studies suggest that cold-water swimming may have a beneficial effect on these components of the blood, potentially improving overall health and wellbeing.
  • Other studies (Study 2, Study 3) used questionnaires to examine the impact of cold-water swimming on wellbeing, fatigue, pain and mental health. Study 2 found that swimmers who participated in cold-water swimming had higher levels of vigour and less fatigue compared to the group who did not swim in cold water. Additionally, those who engaged in winter swimming reported a reduction in pain symptoms. These findings suggest that cold-water swimming may have a positive impact on physical wellbeing.
  • Study 3 did not find any significant differences in mental health between individuals who participated in cold-water swimming and those who did not. This suggests that while cold-water swimming may have benefits for physical wellbeing, it may not necessarily lead to improvements in mental health.
  • The above findings suggest that repeated cold-water swimming can lead to adaptive mechanisms that offer various benefits, such as improved immune response, mood regulation, and pain tolerance, despite the initial stress response that exposure to cold water can trigger. However, further research is necessary to understand the underlying mechanisms of these effects fully and to determine safe and effective strategies for incorporating cold-water exposure into one’s lifestyle.

Things to Remember

  • Opinions alone are not a reliable basis for claims about the effects of treatments.
  • Beware of claims that are based on a single study. Ask if other studies examine the same question and, ideally, if there a careful summary of all the relevant studies.
  • Whenever possible, use up-to-date summaries (systematic reviews) of fair comparisons to inform decisions.


  • Lead Researcher: Dr Caoimhe Madden, Postdoctoral researcher, Evidence Synthesis Ireland, School of Nursing and Midwifery, University of Galway  
  • Reviewed by: Prof. Declan Devane, Professor of Health Research Methodology, Deputy Dean, College of Medicine, Nursing and Health Sciences, University of Galway, Scientific Director, HRB-Trials Methodology Research Network Director, Evidence Synthesis Ireland. Director, Cochrane Ireland 
  • Topic advisor: Prof. Emma Wallace, Professor of General Practice, Dept of General Practice, University College Cork & General Practitioner, Parklands Surgery, Commons Road, Cork.   
  • Public and Patient advisor: Deirdre Mac Loughlin, Public and Patient Involvement in research (PPI) advisor, PPI Ignite, NUI Galway  
  • Journalist Advisor: Dr Claire O’Connell, PhD in cell biology, MSc Communication. Contributor to The Irish Times, writing about health, science and innovation.   

Conflict of Interest Statement: The authors have no financial or other conflicts of interest for this health claim summary.