Contrast therapy improves circulation

During a session, alternating hot and cold makes blood flow in the skin and in the muscle underneath rise with each warm phase and fall with each cold one, and in a few small studies blood flow was still above its starting level minutes to a day later. Whether repeated sessions change circulation in a lasting way has been tested in four small studies over several weeks, and three found no change: artery function did not change after 8 weeks of sauna sessions that included a brief cold shower (21 adults with stable coronary artery disease) or after 5 weeks of hot and cold hand baths (8 men), and a test of small blood vessels did not differ after 4 weeks of contrast showers (60 athletes). The fourth, in 40 climbers, found better skin blood flow after 8 weeks with a device that also squeezed the arm with air pressure.

Where alternating has been compared with steady warmth, it has not clearly added anything. In two small studies of resting legs, water held at one temperature (40 degrees C in one, near skin temperature in the other) raised blood flow more than contrast water did, and in the second, blood flow in the main thigh artery did not change at all during 16 minutes of contrast water. In a trial of a hot and cold compression cuff, skin blood flow five minutes after a session was as high with heat alone as with alternating heat and cold. Two studies from one laboratory, which may share some participants, found the reverse in adults without diabetes: foot skin blood flow was higher with 3 minutes warm and 1 minute cold than with continuous warm water, in adults averaging 24 and in adults averaging 55, though about a third lower in the older group with either bath. In one of them, 14 people with type 2 diabetes had lower blood flow throughout and no difference between contrast and warm water. For people whose circulation is already impaired, cold is the part that carries risk: cold brings on blood vessel spasms in Raynaud phenomenon, and sudden cold immersion can disturb heart rhythm. The literature search for this claim found no study of repeated contrast sessions in people with peripheral artery disease or diabetes-related circulation problems that measured circulation over time. In heart disease there is one: 41 adults with stable coronary artery disease were randomized to 8 weeks of sauna sessions that included a brief cold shower or to carrying on as usual, and artery function in the sauna group did not change.

The single-session studies were small and mostly in young, healthy people. In 24 men, blood flow in the lower leg rose and fell throughout 20 minutes of contrast water, while warm water at 40 degrees C changed it significantly more than either no treatment or contrast, and cold water at 13 degrees C did not significantly lower it. In 10 athletes standing in water to the thigh, blood flow in the thigh artery rose 75 percent in water near skin temperature, fell 16 percent after 7 minutes in cold water, and did not change during contrast water. In 16 young adults who alternated one lower leg between 25 and 42 degrees C water, skin and knee-artery blood flow rose above baseline after every routine, most with two rounds of 6 minutes each, and the authors concluded that the length of each hot period mattered more than the number of switches. In 34 young adults alternating one hand between 40 and 18 degrees C water, the swing in arm artery blood velocity was about half as large in the second and third rounds as in the first. In 10 adults, a sensor over the calf showed oxygenated blood in the muscle rising in each hot phase and falling in each cold one during a 30-minute contrast bath, ending higher than it started. In 40 athletes given one forearm session with a compression cuff, skin blood flow five minutes later was about double the sham level after heat alone and after alternating heat and cold, and less than half the sham level after cold alone; a day later the differences between the groups were small. A 2009 review of 10 contrast bath studies going back to 1938, in healthy volunteers and people with rheumatoid arthritis, diabetes or ankle injuries, concluded that contrast baths may raise blood flow near the skin and skin temperature, that the evidence on swelling is conflicting, and that no link to better function has been shown.

Over weeks, the evidence is thinner. In a 2026 review of 21 studies of whole-body routines, mostly sauna followed by cold water or cold air, only 1 was a randomized trial and 14 had no comparison group; repeated sessions produced signs of adapting to heat, such as a lower resting body temperature, but little evidence of a change in resting blood pressure or heart rate. In 60 combat sport athletes randomized to a contrast shower or a lukewarm shower after every training session for 4 weeks, the blood flow response after a brief cuff test did not differ between the groups. In 8 men who alternated one hand between 8 and 43 degrees C water for an hour three times a week for 5 weeks, finger temperature during a cold water test and the widening of the arm artery after a cuff test were unchanged. In one 8-week trial, 40 amateur climbers who had 27 forearm sessions with a device alternating 3 and 45 degrees C had better skin blood flow at 24 and 48 hours and a larger blood flow response after a brief cuff test at 8 weeks than climbers who rested. The device also squeezed the arm with air compression, participants knew which group they were in, and the authors state that the results do not show improved function of the blood vessel lining.

During contrast routines, heart rate, cardiac output and blood pressure change. The 2026 review describes rises in heart rate and cardiac output and shifts in blood pressure during a session. A review of sudden cold water submersion describes heart rhythm disturbances, including in healthy volunteers, particularly when the face goes under. A review of sauna bathing names unstable angina, a recent heart attack and severe aortic stenosis as reasons to avoid sauna heat, and reports that alcohol during sauna use raises the risk of low blood pressure, abnormal heart rhythm and sudden death. The US National Library of Medicine's MedlinePlus page on Raynaud phenomenon says most people keep symptoms under control by avoiding getting cold. Its page on diabetic foot problems says diabetes can damage the nerves and blood vessels of the feet, causing loss of feeling and poor blood flow, and its foot care list includes washing in warm water without soaking and protecting the feet from heat and cold. The contrast shower and device trials enrolled healthy athletes aged 18 to 40. None of the sources here reports on contrast therapy in pregnancy, in older adults with narrowed leg arteries, or in people with reduced feeling in their feet, so they do not show whether it suits any of these groups.

Apart from one single-session study in people with type 2 diabetes and two studies in the 2026 review that enrolled people with heart disease, these studies were done in healthy people. None looked at contrast therapy as a way to manage a diagnosed circulation problem such as leg swelling, varicose veins or narrowed leg arteries. A few small studies in Indonesia, none of them randomized and none cited here, gave contrast foot baths together with leg raising or foot massage to people with heart failure and swollen legs and reported less swelling graded by hand; none measured blood flow. None of the sources here shows whether contrast therapy is safe for people with heart failure. The 2026 review includes one heart failure study, a single session of sauna, a cool shower and a few seconds in 12 degrees C water in 12 men averaging 62, in which heart rate rose from about 73 to 90 beats a minute and cardiac output from about 4.4 to 6.3 liters a minute, and the review reports nothing on side effects. A 2023 review of 20 randomized trials of Kneipp hydrotherapy, a 19th-century German system of mostly cold water treatments, included mild heart failure among its conditions, found that only about half of its trials reported on safety, and states that no clear conclusion on safety can be drawn.