Cold and Heat Exposure: Cold Plunges, Saunas and Biohacking Claims
What research shows about cold plunges, cold showers and saunas, which benefit claims are supported, and the heart, breathing and drowning risks to know about first.
Content last updated . This page has not been medically reviewed.
Safety first
Cold water and heat both put real strain on the heart and circulation. This page gives no temperatures or times, because safe limits depend on the person. Talk with a clinician before starting if you have heart disease, high or low blood pressure, take blood pressure medicines, are pregnant, or are an older adult. Never practice cold immersion alone or in open water you do not know. For general hydrotherapy information see Hydrotherapy and hydrotherapy safety.Evidence labels used: established, promising but limited, mixed, insufficient evidence, marketing claim.
Cold Exposure
The main danger: cold shock. Sudden skin cooling in cold water triggers the cold shock response, which can be life-threatening. [1] An NHS ambulance service explains that it narrows skin blood vessels, causes an involuntary gasp, can make breathing rates change uncontrollably, and can cause heart attacks even in relatively young and healthy people. [2] Its advice if you unexpectedly end up in cold open water is to wait for the first effects to pass, then float on your back and call for help. [2]Other risks: a literature review found immersion pulmonary edema (fluid in the lungs) is rare but can recur and be fatal, with cold water, exercise and age over 50 among the risk factors. [3] People with a past episode should get cardiopulmonary checks and avoid cold water. [3]
What benefits are claimed, and what is known.
| Claim | Evidence | Label |
|---|---|---|
| Less muscle soreness after exercise | Cochrane review of 17 small, low-quality trials found some benefit versus rest; adverse events mostly not monitored [4] | promising but limited |
| Fewer sick days | A trial of 3,018 adults found 29% less self-reported sickness absence with a routine cold shower, but no difference in illness days [5] | mixed |
| Less stress, better sleep and mood | A 2025 meta-analysis of 11 trials found lower stress at 12 hours but not at other times, improved sleep quality and quality of life, and no mood benefit; it noted few trials and small samples [6] | mixed |
| Reduced inflammation | The same meta-analysis found inflammation measures rose right after immersion and at 1 hour [6] | no good evidence of benefit (an acute rise was seen) |
Fat loss, longevity and "reset" claims. Proper evidence not found in the sources we read for cold exposure causing fat loss or longer life in people.
Heat Exposure
Saunas. In a Finnish cohort of 2,315 middle-aged men followed about 21 years, those who reported more frequent sauna sessions had lower risks of sudden cardiac death and death from any cause. [7] This is an observational association: the men were not randomly assigned, so it cannot prove saunas caused the difference, and the study included only men from one region. One review calls sauna use a probable means to extend healthspan based on observational, interventional and mechanistic data. [8] We rate this promising but limited. For types of sauna see saunas and steam rooms.Blood pressure. A 2026 narrative review found that heat therapies such as saunas and hot water immersion produced transient drops in blood pressure; most studies lacked control groups, the long-term blood pressure benefit is unproven, and safety margins in frail older adults and beta-blocker users are insufficiently defined. [9] Serious acute events were rare in the studies reviewed. [9]
Who should check first. Anyone with heart or blood pressure conditions, those taking medicines that affect blood pressure, older adults, and people who are pregnant. We did not find sources in this session for specific pregnancy or alcohol rules, so ask your clinician.
Stop signs
Leave the cold or heat and get help for chest pain, fainting, severe dizziness, confusion, trouble breathing or coughing up pink or bloody fluid. In a US emergency call 911.Frequently asked questions
Is a cold plunge safe for everyone?
No. Cold water can trigger cold shock that affects the heart and breathing. [2] People with heart conditions should ask a clinician first.
Do saunas extend life?
Observational data link frequent sauna use with lower mortality in Finnish men, but that does not prove cause. [7]
Do cold showers help immunity?
One trial found fewer sick days taken off work but no change in days ill. [5] The immune evidence is mixed.
Can I do this alone?
Cold water drowning risk is real; the ambulance service advises staying calm and floating if you are shocked by cold water. [2] Do not practice alone.
References
- Frontiers in Psychology 2018, Acute Anxiety Predicts Components of the Cold Shock Response on Cold Water Immersion. Read 2026-10-22.
- East Midlands Ambulance Service (NHS), Thinking of swimming in open water? Don't risk it. Read 2026-10-22.
- The Physician and Sportsmedicine 2019, A literature review of immersion pulmonary edema. Read 2026-10-22.
- Cochrane Database of Systematic Reviews 2012, Cold-water immersion (cryotherapy) for preventing and treating muscle soreness after exercise. Read 2026-10-22.
- PLoS One 2016, The Effect of Cold Showering on Health and Work: A Randomized Controlled Trial. Read 2026-10-22.
- PLoS One 2025, Effects of cold-water immersion on health and wellbeing: a systematic review and meta-analysis. Read 2026-10-22.
- JAMA Internal Medicine 2015, Association between sauna bathing and fatal cardiovascular and all-cause mortality events. Read 2026-10-22.
- Experimental Gerontology 2021, Sauna use as a lifestyle practice to extend healthspan. Read 2026-10-22.
- Complementary Therapies in Medicine 2026, Acute blood pressure responses and safety considerations in heat therapy interventions: a narrative review. Read 2026-10-22.