Researchers looked at the increasingly popular cold water immersion therapies - such as taking cold showers or sitting in an ice bath - to see whether claims of positive effects on health and well-being are backed by science.

Cryotherapy - the application of ice, cold water or cold air to the body - has been used for centuries to promote health. In fact, the more than 3,000-year-old Edwin Smith Papyrus, the oldest known scientific work on spinal injuries in existence, mentions the use of cold water immersion to treat spinal trauma.

The practice of cold water soaking certainly has its devotees. But is taking a daily soak in cold water, whether that's a cold shower, swimming in icy ocean water, or sitting in a tub filled with ice, really good for your health? To answer this question, researchers from the University of South Australia (UniSA) conducted the most comprehensive review and meta-analysis on this topic to date.

Tara Cain, a research associate at the Alliance for Research in Exercise, Nutrition and Activity (ARENA) at the University of South Australia and first and corresponding author of the study, said: "Cold water immersion has been widely studied and used in sports to aid athlete recovery, but despite its increasing popularity in the health and wellbeing community, little is known about its effects in the general population."

The researchers reviewed and analyzed 11 studies published between 2014 and 2023, involving a total of 3,177 healthy adults. Ten of the studies looked at the effects of soaking in ice baths or cold water baths, and one study looked at the effects of cold showers. Only studies in which participants were immersed in water at or above chest level were included. Water temperatures vary from 7°C to 15°C (45°F to 59°F), and the soaking time is a minimum of 30 seconds and a maximum of two hours. Outcomes of particular interest to the researchers relate to sleep, stress, fatigue, energy, skin health, immunity, inflammation, mental health, depression, anxiety, mood, attention, alertness or focus.

"In this study, we noticed a series of time-related results," Cain said. "First, we found that cold water immersion reduced stress levels, but only within 12 hours of cold water exposure. We also noticed that participants who took 30-, 60-, or 90-second cold baths [for 30 days] had slightly higher quality-of-life scores. But again, after three months, these effects disappeared."

"One study reported that participants who took regular cold showers had a 29% reduction in sick days. We also found that cold water immersion was associated with improved sleep, but the data were limited to men, so its wider application is limited. While there have been claims that the cold water immersion experience can improve immunity and mood, we found very little evidence to support these claims."

Somewhat counterintuitively, the researchers found that cold water immersion was associated with significant increases in inflammatory markers immediately and one hour after the immersion.

"This may seem paradoxical at first glance because we know that elite athletes often use ice baths to reduce inflammation and muscle soreness after exercise," said Ben Singer, Ph.D., senior author of the study and an ARENA researcher. "The immediate spike in inflammation is the body's response to the stressor of cold. It helps the body adapt. Response and recovery, similar to exercise, can cause muscle damage before making the muscles stronger, which is why athletes experience increased inflammation in the short term. With this in mind, people with pre-existing health conditions should be extra cautious when participating in cold water immersion experiences, as the initial inflammation may have adverse health effects."

The studies reviewed as part of this study were conducted in Australia, Lithuania, the Netherlands, Switzerland, Japan, the United States and Finland. Understanding the long-term benefits and risks of cold water immersion on health and well-being will require further randomized controlled trials using large and diverse samples of participants. In addition, it would be of interest to study the dose-response relationship between cryotherapy and health, including optimal temperature, soaking time and frequency.

"Whether you are an elite athlete or an everyday health seeker, it is important to understand the effects of cryotherapy on the body," says Cain. "Right now, there aren't enough high-quality studies to say who benefits most, or what the ideal approach to cold water immersion is."

The research was published in the journal PLOSOne.