Contrast therapy: sauna and cold plunge benefits, evidence and safety

Contrast therapy means alternating heat and cold: a few minutes in a sauna, hot tub or hot shower, then a cold plunge, ice bath or cold shower. Many people repeat the cycle several times.

In the sauna or hot water, the blood vessels in your skin widen, your heart beats faster and you sweat. Cold water does the opposite: the skin’s blood vessels narrow and, in the first minutes, your breathing and pulse jump suddenly. That contrast is what people are after, and it is also why it isn’t for everyone.

This is an evidence and safety guide: sauna and cold plunge are not part of the listed inclusions of The Health Initiative’s wellness retreat.

The most cited study of sauna benefits is Laukkanen and colleagues, published in JAMA Internal Medicine in 2015. It followed 2,315 Finnish men aged 42 to 60 for a median of 20.7 years. Compared with men who used a sauna once a week, those who used it 4 to 7 times a week had a lower risk of sudden cardiac death, fatal heart disease and death from any cause. Sessions longer than 19 minutes were also linked with less sudden cardiac death than sessions under 11 minutes.

This is an observational study: it shows an association, not proof that the sauna caused the difference. Men who were able to use the sauna often may already have been healthier, and all of them were middle-aged men in Finland, where sauna is part of daily life. A review in The American Journal of Medicine concludes that most healthy adults tolerate sauna well, and that some studies suggest it may help lower blood pressure in people with hypertension, but more data are needed to confirm it.

Most cold water immersion studies look at recovery after exercise. A meta-analysis of 9 randomized trials (Machado and colleagues, 2016) found cold water can be slightly better than passive rest for muscle soreness, with the largest effect at 11 to 15 °C (52 to 59 °F) for 11 to 15 minutes. A Cochrane review of 17 small trials reached a similar conclusion but rated the quality of the evidence as low.

A larger meta-analysis of 52 studies (Moore and colleagues, 2022) found cold water immersion improved muscle soreness and perceived recovery 24 hours after hard exercise and helped muscle power recover, but did not improve the recovery of strength. For contrast therapy itself, a review of 18 trials (Bieuzen and colleagues, 2013) found less muscle soreness than with rest, but no clear advantage over other recovery methods such as cold water alone, warm water or stretching; every trial had a high risk of bias.

If you lift weights: in a 12-week trial (Roberts and colleagues, 2015), men who sat in cold water for 10 minutes after each workout gained less strength and muscle than men who did an active cool-down. A 2024 meta-analysis (Piñero and colleagues) found some evidence pointing the same way. If your goal is strength or muscle, you may want to skip the cold plunge right after training.

This describes what researchers used; it is not a recommendation for you. In the 2013 contrast water therapy review:

Puerto Rico’s Department of Health explains that the body cools itself by sweating, but in some conditions sweating isn’t enough and body temperature rises fast. Heat and humidity here already make your body work; the National Weather Service’s heat index measures how hot it really feels once humidity is factored in. A sauna on top of a hot, humid day adds more heat stress.

If you use a sauna here, plan your hydration: the CDC advises drinking plenty of fluids and carrying a water bottle through the day. The CDC also notes that heat is riskier for pregnant women, people with heart disease, adults 65 and older, and people exercising outdoors. Some medicines raise your risk in the heat; ask your doctor or pharmacist about yours.

No. Sauna and cold plunge are not on the list of inclusions of The Health Initiative’s wellness retreat. What the retreat includes: lodging and meals; medical care and labs (a physician assessment, and lab work when clinically appropriate); mobility coaching, meditation and breathwork, and nutrition sessions; and island activities and airport transfers.

All of the medical care is provided by Dr. Diana Nieves Castro, a general practice physician licensed in Puerto Rico. To read about what the sessions do cover, see breathwork and mobility vs flexibility. For what the retreat does include, see a typical day at the retreat.