What Does Cold Water Immersion Actually Do?

Cold water immersion, from ice baths to cold plunges and winter swimming, has a strong reputation and a thinner evidence base. Its effects on the body in the first minutes are well described, and some of them are dangerous. Its longer-term benefits are less certain: the trials are small, and one well-designed study found that plunging after strength training reduced muscle gains.

This article is general information, not medical advice. Cold water can trigger heart rhythm problems; if you have heart disease or high blood pressure, ask your doctor first.

What Happens in the First Minutes

Sudden immersion in cold water sets off the cold shock response: a gasp, rapid breathing you can’t control, and a surge in heart rate and blood pressure. In his review “Cold water immersion: kill or cure?”, Tipton and colleagues describe it as the main cause of deaths soon after falling into cold water, through inhaling water or heart rhythm problems, and note that it’s greatest in the first few minutes and lessens with repeated exposure.

What the Evidence Shows

• Cold showers and sick days. In a trial of 3,018 Dutch adults, Buijze and colleagues asked people to end their usual hot shower with 30, 60, or 90 seconds of cold for 30 days. Those who did reported 29% fewer days off work sick, but no fewer days of illness, so they may have felt well enough to work rather than being ill less.
• After strength training. Roberts and colleagues had 21 active men strength train twice a week for 12 weeks, following each session with 10 minutes in cold water or an active cool-down. The cold water group gained less muscle mass and strength, and a second experiment showed it dampened the muscle’s growth signalling after a session.
• Broader claims. A 2022 systematic review by Espeland and colleagues found reports of effects on inflammation, insulin sensitivity, and mood, but that most studies were small, often in one sex, and used different temperatures, so clear conclusions weren’t possible.

If building muscle is your goal, the Roberts study is a reason to keep plunges away from strength sessions.

Trying It Safely

• Never alone in open water, and get in gradually rather than jumping.
• Control your breathing through the first minute until the gasping settles.
• Keep it short. A few minutes is enough; numbness, confusion, or shivering you can’t stop mean get out.
• Rewarm gently with dry clothes and movement, not a very hot shower straight away.
• Avoid alcohol before or after.

Following It in Kaizora

Log a cold plunge as an activity on Activities, and Kaizora adds its duration to Cold Plunge Time and counts it in Cold Plunge Sessions. Both are summed. On Correlations, putting cold plunges beside Mood or Total Sleep Time by day lets you see whether they go together for you, which is the kind of evidence a personal experiment can give; see Comparing Metrics.

The Short Version

• The cold shock response in the first minutes is the main danger: gasping, a racing heart, and high blood pressure.
• Cold showers cut self-reported sick days in one trial, without fewer days of illness.
• Plunging after strength training reduced muscle and strength gains in one trial.
• Most other claimed benefits rest on small studies.

Sources

• Tipton MJ et al., “Cold water immersion: kill or cure?” Experimental Physiology 102, no. 11 (2017): 1335–1355. doi:10.1113/EP086283
• Buijze GA et al., “The effect of cold showering on health and work: a randomized controlled trial,” PLOS ONE 11, no. 9 (2016): e0161749. doi:10.1371/journal.pone.0161749
• Roberts LA et al., “Post-exercise cold water immersion attenuates acute anabolic signalling and long-term adaptations in muscle to strength training,” Journal of Physiology 593, no. 18 (2015): 4285–4301. doi:10.1113/JP270570
• Espeland D, de Weerd L, Mercer JB, “Health effects of voluntary exposure to cold water: a continuing subject of debate,” International Journal of Circumpolar Health 81, no. 1 (2022): 2111789. doi:10.1080/22423982.2022.2111789