Short read
Owen and colleagues at Bangor University ran a counterbalanced crossover study, published in Experimental Physiology in 2026. 16 healthy adults, 8 women and 8 men with an average age of 31, completed two visits at least 48 hours apart. Each visit consisted of two sauna bouts of 15 minutes at 85 degrees with a 10-minute cooling break, then 30 minutes of seated recovery. In one arm the break was spent in ambient air at 23 degrees; in the other, the same break included 90 seconds of whole-body immersion in water at 20 degrees. The setting was a public Finnish sauna, not a laboratory.
Compared with the air-only break in the same people, values at the end of the second bout were lower after the cold water break: core temperature 37.55 against 38.03 degrees, a difference of 0.48 degrees (confidence interval 0.25 to 0.71), and heart rate 108 against 125 beats per minute, a difference of 17 beats (6.6 to 26). Systolic and mean arterial pressure did not differ; diastolic pressure was lower with air-only cooling at the end of the breaks and 20 minutes into recovery. Sweat loss was 0.56 against 0.72 kilograms, without a robust difference. Participants felt less hot with the plunge.
The study had 16 healthy adults and one session per condition. Sauna temperature varied by seat between about 70.5 and 85.5 degrees, other guests poured water on the stove, and humidity was measured only at the end of the bouts. The study was not preregistered, and cycle phase was not standardised.
The finding cuts both ways. The plunge made the second bout more tolerable and lowered the risk of heat exhaustion, and it also lowered the thermal load that makes up the heat stimulus. What this weaker stimulus means over weeks, the study does not show.