Cold Showers vs Hot Showers: What the Evidence Says, Plus Cold Plunges

Cold showers are sold as a cure for everything from a slow metabolism to a weak immune system, and hot showers get treated as the lazy option. The research tells a more useful story. Cold water has one well-supported job, taking the edge off next-day soreness after hard conditioning, and one well-documented cost, blunting the muscle and strength gains you train for if you use it right after lifting. Hot water has the better sleep evidence and, in large population studies, the better heart story. This guide goes through what each temperature does and does not do, what the famous numbers (29 percent fewer sick days, metabolism up 350 percent) actually came from, where cold plunges fit, and how we schedule both for clients who train.

This is general information from published research, not medical advice. If you have heart disease, high blood pressure or poor circulation, read the safety section before trying any of it.

The short version

• Cold water after hard exercise reduces soreness. Across 17 small trials, cold water immersion cut next-day soreness with moderate effect sizes versus rest. The studied dose is 10 to 15 minutes immersed at 10 to 15 C, not a two-minute shower, and we found no trial of a cold shower for soreness.
• Cold water right after lifting blunts your gains. In a 12-week trial, the group that skipped the ice bath grew their fast-twitch fibers 17 percent; the ice-bath group did not. Pooled across trials, strength adaptations fell by a moderate amount while endurance adaptations were untouched.
• The 29 percent fewer sick days is real, and narrower than it sounds. In 3,018 adults, a cold finish to the shower cut self-reported sick days by 29 percent, but people did not report fewer days of illness, and anxiety did not change. The 30-second arm did as well as 90 seconds.
• Metabolism up 350 percent came from an hour in 14 C water, to the neck. Our arithmetic puts a two-minute cold shower at roughly 8 extra calories. A systematic review of 47 brown-fat trials calls cold exposure “an unlikely sustainable therapy to combat obesity.”
• The “cold builds immunity” studies are breathing studies. When the Wim Hof method was split into its parts, the breathing drove the anti-inflammatory effect; cold alone changed one marker out of eight.
• Hot water wins on sleep. A warm bath or shower at 40 to 42.5 C, one to two hours before bed, shortens the time to fall asleep and improves sleep quality across 17 studies.
• Safety is not fussiness. Sudden cold immersion can trigger arrhythmias even in healthy people through “autonomic conflict”; the “one minute per degree” rule is a myth; and 140 F tap water burns in about six seconds.

What cold water does, with evidence

Soreness after hard training

This is the one claim that survives scrutiny, with caveats about dose. Cochrane’s review of 17 trials (366 participants) found cold water immersion after exercise reduced soreness versus passive rest, with pooled standardized effects of -0.55 at 24 hours, -0.66 at 48 hours and -0.93 at 72 hours; the authors rated study quality low and noted that most trials did not monitor adverse events (Bleakley and colleagues, Cochrane, 2012). A 52-study meta-analysis found cold immersion improved next-day muscular power after both eccentric and high-intensity exercise, reduced soreness and creatine kinase after high-intensity work, and had “no significant effect on strength” recovery (Moore and colleagues, Sports Medicine, 2022). The most recent pooled analysis of 20 studies agreed on the immediate effect (soreness SMD -0.59 right after) but found the 24 and 48 hour effects weaker and, in its sensitivity analysis, not statistically significant (Xiao and colleagues, Frontiers in Physiology, 2023).

Two things to notice. First, the benefit is for soreness and power after hard conditioning, which matters if you have a second session tomorrow and matters much less if you do not. Second, the dose. The commonly cited target, attributed to a 2016 meta-analysis, is 11 to 15 C for 11 to 15 minutes, immersed. A two or three minute shower at whatever your tap delivers, which in a Manhattan summer is probably well above 15 C (we found no published figure; a cheap thermometer under the tap settles it), is a small fraction of that, and we found no randomized trial of a cold shower for post-exercise soreness. If you want the recovery effect, it is an ice bath or a plunge, not a shower.

Contrast showers

Alternating hot and cold beat doing nothing for soreness in a meta-analysis of 18 trials (SMD -0.51 at 24 hours) but for soreness showed no significant difference at any time point against cold-only immersion, and none against active recovery, compression or stretching; every included trial was at high risk of bias (Bieuzen, Bleakley and Costello, PLOS ONE, 2013). Contrast showers are fine. There is no evidence that the alternating itself adds anything.

Alertness and mood, for a while

Cold water wakes you up; nobody disputes that. The question is what else it does. In 33 healthy adults, a single five-minute head-out immersion in 20 C water raised positive mood and lowered negative mood, with people reporting feeling “more active, alert, attentive, inspired, and proud,” but the study had no control group and was not randomized, and its authors say replication is needed (Yankouskaya and colleagues, Biology, 2023). A 2025 meta-analysis of 11 randomized trials (3,177 people) found cold immersion lowered self-reported stress at the 12-hour mark (SMD -1.00) but not immediately, at one hour, or at 24 or 48 hours, and raised inflammation markers immediately and at one hour (SMD 1.03 and 1.26), which the authors describe as “an acute inflammatory response” (Cain and colleagues, PLOS ONE, 2025). You will likely feel more alert and upbeat afterward. Whether that is worth anything beyond the afternoon is not established.

The “cold showers treat depression” idea traces to a 2008 article in Medical Hypotheses, a journal for untested ideas, not a trial. No randomized trial designed to test whether cold water treats clinical depression has reported results; the first full-scale one, a 480-person trial of outdoor swimming for depression in England, is under way and has not yet published findings (OUTSIDE 2 protocol, NIHR Open Research, 2026). Until it reports, the depression claim is ahead of the evidence.

What cold water does not do

It does not make you sick less often

The most-cited cold-shower study randomized 3,018 Dutch adults to end a warm shower with 30, 60 or 90 seconds of cold water for 30 days, or to shower normally. Self-reported sickness absence from work fell 29 percent (incidence rate ratio 0.71). But the number of days people reported being ill did not differ between groups, anxiety did not differ, and the small quality-of-life gain at 30 days was gone at 90 days. The 30-second group did as well as the 90-second group (Buijze and colleagues, PLOS ONE, 2016). The honest reading: people who took cold showers called in sick less. They were not sick less. The 2025 meta-analysis above found no effect of cold immersion on immune markers.

The immune claim belongs to breathing, not cold

The study behind “cold exposure trains your immune system” is the 2014 Wim Hof experiment, in which 12 volunteers trained for 10 days in meditation, breathing and cold exposure and then blunted an injected bacterial toxin’s effects better than 12 controls (Kox and colleagues, PNAS, 2014). That study tested the whole package. The same group later split it apart in a 48-man trial: breathing alone reduced IL-6 by 34 percent and IL-8 by 14 percent, the combination did more, and cold exposure alone changed only one of the eight inflammatory markers measured (Zwaag and colleagues, Psychosomatic Medicine, 2022). The breathing did the work. The cold, at most, helped it along.

It does not meaningfully raise your metabolism

The “350 percent” figure is real. In a study of young men, one hour of head-out immersion in 14 C water raised metabolic rate 350 percent; at 20 C the rise was 93 percent and at 32 C there was no change. Noradrenaline rose 530 percent; adrenaline, despite what the posts say, was unchanged (Sramek and colleagues, European Journal of Applied Physiology, 2000). Scale that to a shower. Our arithmetic, with a resting rate of about 1.2 kcal per minute: a 350 percent increase is about 5.4 kcal per minute, so two minutes is about 11 kcal against about 2.4 at rest, roughly 8 extra calories, and that is an upper bound because a shower wets part of you, is warmer than 14 C and the metabolic rise is not instant. Think a bite of a banana, not a workout. Brown fat is real and trainable: 10 days of daily cold exposure recruited it and raised heat production without shivering in a Dutch study (van der Lans and colleagues, Journal of Clinical Investigation, 2013). But a systematic review of 47 clinical trials concluded that cold exposure “appears to consistently activate BAT and induce thermogenesis” and is still “an unlikely sustainable therapy to combat obesity,” with weight changes described as minimal (Perez and colleagues, Frontiers in Endocrinology, 2022).

It blunts the gains you lift for

This is the finding that should change what athletes do. In a 12-week trial, 21 men lifted twice a week and then either sat in cold water for 10 minutes or did active recovery. Strength and muscle mass increased more in the active-recovery group; in that group only, type II fiber area rose 17 percent and myonuclei per fiber rose 26 percent. The authors wrote that using cold immersion “as a regular post-exercise recovery strategy should be reconsidered” (Roberts and colleagues, Journal of Physiology, 2015). A 7-week trial found the same blunting of fiber growth, though not of one-rep-max strength, and concluded cold immersion “should therefore be avoided if muscle hypertrophy is desired” (Fyfe and colleagues, Journal of Applied Physiology, 2019). Pooled across eight studies, lifting alone produced a hypertrophy effect of 0.36; lifting plus cold immersion, 0.14 (Pinero and colleagues, European Journal of Sport Science, 2024). And across trials of regular use, cold immersion alongside strength training cut strength adaptations by a moderate amount (SMD -0.60) while having no effect on aerobic adaptations (SMD -0.07 for maximal aerobic power, 0.00 for time-trial performance) (Malta and colleagues, Sports Medicine, 2021).

That gives a clean rule. Cold after cardio or conditioning: fine, and useful if you are sore. Cold right after lifting, when muscle or strength is the goal: skip it.

What hot water does, with evidence

Sleep

This is the best-supported shower claim in either direction. A systematic review of 17 studies (13 pooled) found that a warm bath or shower at 40 to 42.5 C (104 to 108.5 F), taken one to two hours before bed, improved self-rated sleep quality and sleep efficiency and shortened the time to fall asleep, with as little as 10 minutes of warming being enough (Haghayegh and colleagues, Sleep Medicine Reviews, 2019); a USC press summary put the sleep-onset gain at about 10 minutes, with 90 minutes before bed as the sweet spot (USC News). The mechanism is the opposite of what people assume: warm water pulls blood to the hands and feet, which speeds heat loss and lets core temperature fall, and a falling core temperature is a signal for sleep. By the same logic, a cold shower, which constricts skin vessels, should work against that drop; no trial has tested it directly. There is no trial of cold showers before bed; the only sleep data in the 2025 meta-analysis came from a single study of 20 men. If you like cold water, take it in the morning. Before bed, the evidence says warm. Our sleep guide has the rest of the routine.

The heart, in population studies

Heat has a cardiovascular story that cold does not, with the caveat that it comes from observational studies in bathing cultures. In 30,076 Japanese adults followed for about 19 years, near-daily hot baths (Japanese-style tub bathing) were associated with 28 percent lower cardiovascular disease risk (hazard ratio 0.72), 26 percent lower stroke risk and 46 percent lower risk of brain hemorrhage compared with bathing twice a week or less (Ukai and colleagues, Heart, 2020). In 2,315 Finnish men followed for about 21 years, four to seven sauna sessions a week was associated with a 63 percent lower rate of sudden cardiac death than one session a week (hazard ratio 0.37) (Laukkanen and colleagues, JAMA Internal Medicine, 2015). These are associations: people who bathe daily or sauna five times a week differ from people who do not in ways a study cannot fully adjust for. They are not proof that a hot shower protects your heart. They are a reason to stop treating hot water as the lazy option.

Muscles

Heat is not anti-growth the way cold is. A review of heating for recovery found some support for warming muscle before exercise to limit soreness, more variable results for heat after exercise, and early evidence that heating muscle “may also enhance the benefits of strength training for improving muscle mass” (McGorm and colleagues, Sports Medicine, 2018). A warm bath after lifting is, at worst, neutral for adaptation. A cold one is not.

What hot water does not do

Steam does not clear a cold. Cochrane’s review of six double-blind trials of heated, humidified air for the common cold concluded “the current evidence does not show any benefits or harms” (Singh and colleagues, Cochrane, 2017). A steamy shower feels good when you are congested; it will not change the course of the illness. And hot, long showers are the one shower habit dermatologists actually ask you to drop: the American Academy of Dermatology’s advice for dry skin is to “limit baths and showers to five to ten minutes, using warm water” (American Academy of Dermatology).

Cold plunges

A plunge is the studied dose that a shower is not: 10 to 15 minutes immersed at 10 to 15 C is the range the recovery trials used, so everything in the soreness section applies and everything in the gains section applies with more force. Two practical points. Colder is not better: the commonly cited dose (11 to 15 C) and the 7-week Fyfe trial (15 minutes at 10 C) both sit in the 10 to 15 C range, and a cardiologist’s patient guidance puts “50 F is more than cold enough” with sessions of “about five to ten minutes” (Houston Methodist, 2024). And the “one minute per degree Celsius” rule you will see everywhere has no physiological basis; the Outdoor Swimming Society calls it a myth and lists six reasons bodies cool at different rates, from body fat and surface area to how well you slept (Outdoor Swimming Society). We found no credible body that publishes a safe-duration-by-temperature table. Start at one to two minutes, get out while you still feel fine, and warm up slowly afterward.

Safety

Cold. Sudden immersion triggers the cold shock response, a surge of sympathetic drive and fast breathing. If you also put your face in or hold your breath, you trigger the diving response, which slows the heart. Two physiologists call the simultaneous firing of both “autonomic conflict” and note that submersion can induce “a high incidence of cardiac arrhythmias in healthy volunteers,” which may explain some deaths previously attributed to drowning or hypothermia, especially in “some vulnerable individuals” (Shattock and Tipton, Journal of Physiology, 2012). The same group’s review of the therapeutic claims judged that many rest “at the level of anecdotal speculation” (Tipton and colleagues, Experimental Physiology, 2017). Our rules, drawn from that mechanism: never plunge alone, enter slowly rather than jumping in, keep your face out and keep breathing for the first minute, and get out at the first sign of anything other than cold. The cardiologist’s avoid-or-ask-first list, from the Houston Methodist page above, includes heart disease, high blood pressure, diabetes, peripheral neuropathy, poor circulation including Raynaud’s and venous problems, and cold agglutinin disease.

Hot. The Consumer Product Safety Commission recommends setting water heaters to 120 F; at 140 F, tap water causes a third-degree burn in about six seconds, and at 150 F in about two (CPSC, Tap Water Scalds). Manhattan renters do not control the building boiler, so test the tap before stepping under it, and be careful with children and anyone with reduced sensation.

How we schedule it for clients

This is our practical reading of the evidence above, not a protocol from any single study.

• Morning cold shower: if you enjoy it and it helps you feel awake, keep it. Thirty seconds did as much as 90 in the one big trial. Do not expect it to change your immune system, your weight or your mood beyond the afternoon.
• Cold plunge or ice bath: after conditioning, intervals or a race, or on rest days, when soreness is the problem and you have another hard session coming. Ten to 15 minutes at 10 to 15 C, never alone, face out.
• After lifting: no cold water in the hours afterward if muscle or strength is the goal. Active recovery, a walk, or a warm shower instead. The research does not pin down exactly how long to wait; a few hours is a reasonable gap, and the easiest habit is to save cold water for days you are not lifting.
• Before bed on hard-training days: a warm bath or shower, 40 to 42.5 C, about 90 minutes before you want to be asleep. Keep it to 10 minutes if your skin runs dry.
• Contrast showers: fine if you like them; no evidence the alternating does anything a cold finish does not.

If you want this built into a training week, our trainers come to your apartment, building gym or a nearby park in Manhattan and parts of Brooklyn and Queens; get matched with a trainer. For the full picture on recovery between sessions, see our recovery runs guide; for why cold water feels like it does to your nervous system, see our vagus nerve guide.

Frequently asked questions

Is a cold shower or a hot shower better after a workout?

For soreness after a hard conditioning session, cold, and ideally an immersion rather than a shower. After lifting, warm or neutral: cold water in the hours after resistance training blunted muscle fiber growth in both biopsy trials cited above, reduced the pooled hypertrophy effect across eight studies, and blunted strength adaptation in the pooled analysis. Heat after lifting is at worst neutral.

How long should a cold shower be?

In the 3,018-person trial, 30 seconds of cold at the end of a warm shower produced the same result as 60 or 90 seconds. For recovery, no shower length has been tested; the studied dose is 10 to 15 minutes immersed at 10 to 15 C.

Do cold showers burn fat?

Not meaningfully. The 350 percent metabolism figure came from an hour immersed to the neck in 14 C water. Two minutes under a cold tap is roughly 8 extra calories by our arithmetic, and a 47-trial review of brown-fat activation concluded cold exposure is an unlikely therapy for weight loss.

Do cold showers boost immunity?

No trial shows it. The big Dutch trial found fewer self-reported sick days but no fewer days of illness; the 2025 meta-analysis found no effect on immune markers; and when the Wim Hof method was taken apart, the breathing produced the anti-inflammatory effect, not the cold.

Should I take a cold shower before bed?

The evidence points the other way. Warm water one to two hours before bed helps you fall asleep faster across 17 studies, because it speeds the drop in core temperature that signals sleep. Cold water constricts skin vessels and, by the same logic, works against that, though no trial has tested it. Take the cold one in the morning.

How cold should a cold plunge be?

The recovery trials used 10 to 15 C (50 to 59 F), and a cardiologist’s guidance is that 50 F is more than cold enough, for sessions of about five to ten minutes. Colder is not better, the “one minute per degree” rule is a myth, and nobody should plunge alone.

Who should not take cold showers or plunges?

The cardiologist’s list on the Houston Methodist page cited above says to avoid cold plunges if you have heart disease, high blood pressure, diabetes, peripheral neuropathy, poor circulation (including DVT, varicose veins or Raynaud’s), venous stasis or cold agglutinin disease, and to check with a doctor before starting any new practice. Sudden cold immersion can cause arrhythmias even in healthy people, which is why our plunge rules are enter slowly, face out, keep breathing, never alone.