Before the Penguin Plunge, Know What Cold Water Does to Your Body

On the first day of every year, a crowd gathers at Roger Wheeler State Beach in Narragansett, counts down to noon and runs into Rhode Island Sound. The Penguin Plunge, which raises money for Special Olympics Rhode Island⁴, has been held for about five decades and bills itself as one of the original New Year's Day dips in the state. Other New Year's dips have sprung up over the years in towns including Bristol, Tiverton and Matunuck.

For most participants, the plunge is a few seconds of shrieking and a good story. For a growing number of people, cold water has become a regular habit, through year-round ocean swims, backyard tubs or cold showers, often with claims attached about inflammation, immunity and mood. The research supports some of that, and not much of the rest.

What the evidence says

The most comprehensive recent look is a 2025 systematic review and meta-analysis¹ in PLOS ONE from researchers at the University of South Australia. They gathered randomized trials of healthy adults exposed to cold water at or below 15 degrees Celsius, about 59 degrees Fahrenheit, for at least 30 seconds, by shower, ice bath or plunge. Eleven studies with 3,177 participants qualified.

The results were real but narrow. Self-reported stress dropped 12 hours after immersion, though not immediately or a day or two later. Some studies found better sleep quality, though that data came only from men. People who took short daily cold showers reported slightly higher quality of life, and the effect faded by three months.

Inflammation rose right after immersion and an hour later, which surprised some readers because athletes use ice baths to reduce soreness. The authors described it as the body's short-term stress response and suggested people with existing health conditions take extra care.

On mood, they found no significant effect. On immunity, the meta-analysis found no measurable change in immune markers. The one striking result came from a single large Dutch study, a 2016 randomized trial³ in which adults who finished their daily shower with 30 to 90 seconds of cold water took 29 percent fewer sick days from work. Interestingly, they did not report fewer days of actual illness. They seemed to feel well enough to go in.

The first minute

Narragansett Bay and the open coast are cold in winter, with January water along the south coast typically in the upper 30s to low 40s Fahrenheit. At those temperatures, the main danger is not hypothermia, which takes far longer to develop than most people think. It is cold shock.

When cold water hits a large area of skin, the body responds with an involuntary gasp, followed by rapid breathing that is hard to control. Heart rate and blood pressure jump as blood vessels in the skin clamp down. The National Weather Service² warns that this reaction can last for the first few minutes and can cause drowning even in calm water and even in confident swimmers, because a gasp taken with your face underwater pulls water into the lungs.

Safety educators summarize the timeline as one minute to get breathing under control, about ten minutes of useful muscle function before hands and arms weaken, and roughly an hour before hypothermia sets in. The sudden rise in heart rate and blood pressure is why people with heart disease, uncontrolled high blood pressure or rhythm problems face higher risk and should talk with a clinician first.

If you plan to plunge

Organized plunges are the safest version of the experience, with crowds, lifeguards and rescue crews on hand. Wherever you go in, a few habits reduce the risk.

Walk in rather than jumping or diving, and keep your head above water until your breathing settles. Never go alone, and do not swim out. Stay only as long as it takes to say you did it. Wear water shoes, since winter beaches can hide rocks and debris. Have a towel, warm layers and a hat waiting, and change out of wet clothes quickly. Shivering afterward is normal. Confusion or slurred speech is not.

Skip the alcohol beforehand. It impairs judgment and widens blood vessels in the skin, which speeds heat loss. That advice runs against a long New Year's tradition, which is exactly why it is worth repeating.

A reasonable view

If a cold dip makes you feel alert and connected to a community of people who do it with you, the research gives no reason to stop and some reason to think it helps with stress. It does not support claims that it boosts immunity, burns meaningful fat or treats depression. For a dependable winter mood lift, morning light and outdoor time, which we covered in our story on winter light and vitamin D, carry less risk and a stronger evidence base.