The high-heat environment of a sauna raises the body’s core temperature, driving the physiological changes experienced during a session. Saunas are closed spaces designed for thermal stress, with temperatures ranging from 150 to 195°F (65 to 90°C) in traditional models, or 120 to 150°F (49 to 66°C) in infrared versions. This heat exposure forces the body to activate its natural cooling mechanisms. The core temperature rises because the body absorbs more heat than it can immediately dissipate.
How Sauna Heat Transfers to the Body
Heat transfers from the sauna environment into the body through three main physical processes: convection, radiation, and conduction. Convection, the dominant mechanism in traditional dry saunas, is the transfer of heat through the movement of hot air. The hot air circulates and transfers thermal energy directly to the skin’s surface.
Radiation involves the transfer of heat energy via electromagnetic waves from hot surfaces, such as the stove, rocks, or walls. Traditional saunas use hot stones and walls to radiate heat. Infrared saunas rely almost entirely on radiant heat, using specific wavelengths to penetrate the skin and heat the body directly, allowing them to operate at lower air temperatures.
Conduction is the transfer of heat through direct physical contact, such as sitting on a wooden bench. Although wood benches are usually low-density to reduce this effect, the body’s contact with heated air, surfaces, and radiant energy ensures continuous thermal gain. This influx of energy raises the skin temperature first, which then warms the deeper, internal tissues.
The Body’s Cooling System Activation
To manage the thermal load from the sauna, the body immediately activates its complex thermoregulatory system, which is controlled by the hypothalamus in the brain. The first response is vasodilation, a process where the blood vessels near the skin surface relax and widen. This dramatic increase in blood flow to the skin brings heat from the core to the periphery, allowing the body to attempt to dump thermal energy to the surrounding air.
This redirection of blood flow can be significant, sometimes accounting for as much as 30% of the total cardiac output. The increased demand on the heart to pump blood to the skin results in an elevated heart rate, similar to moderate exercise. As the core temperature continues to rise, the body initiates its second cooling mechanism: sweating.
Sweating is controlled by the hypothalamus sending nerve signals to the sweat glands throughout the skin. The sweat produced then cools the body through evaporation; as the liquid water on the skin turns into a gas, it draws a substantial amount of heat away from the body. High humidity can hinder this evaporative process, making the heat feel more intense and potentially increasing the internal temperature faster.
Typical Temperature Increase and Usage Guidelines
A typical sauna session causes the core body temperature to rise by about 1 to 3°C (2 to 5°F). For example, the body’s normal temperature of 98.6°F (37°C) might increase to 100 to 102°F (38 to 39°C) during a 15- to 30-minute session. This induced state of mild, controlled hyperthermia is responsible for many physiological benefits.
To manage this temperature increase safely, a session duration of 15 to 20 minutes is recommended. Exceeding this time, especially without acclimation, increases the risk of heat strain and dehydration. Fluid loss through heavy perspiration can range from 0.23 to 2.3 liters depending on the exposure’s intensity and duration.
Safety Guidelines
Adequate hydration is necessary before and after using the sauna to replace lost fluids and minerals. The maximum recommended temperature for a traditional sauna is typically between 170 and 190°F (77 and 88°C). Listening to the body and exiting immediately if discomfort, dizziness, or lightheadedness occurs is the most important guideline for safe use.