A sauna is a small, insulated room designed to provide intense heat exposure for relaxation and wellness. Whether a sauna is humid depends entirely on the heating system used and the user’s specific practice. The core distinction lies in the difference between dry heat and wet heat, which dictates the resulting humidity levels.
The Baseline: Traditional Dry Heat Saunas
The traditional Finnish-style sauna is fundamentally a dry heat environment. These rooms are typically heated by an electric heater or a wood stove that warms the air and a pile of rocks. The air temperature is maintained at a high level, often ranging between 160°F and 195°F (71°C and 90°C).
In this initial state, relative humidity inside the sauna is intentionally kept very low, usually in the range of 5% to 20%. This low moisture content allows the body to tolerate the extremely high temperatures. The dry air permits sweat to evaporate quickly from the skin, which is the body’s primary cooling mechanism.
This rapid evaporative cooling prevents the high heat from becoming immediately overwhelming. Without this low humidity, the air would feel significantly hotter, and the risk of overheating would be much greater. The dry heat transfers energy primarily through convection from the heated air and radiation from the stove and walls.
Introducing Moisture: The Concept of Löyly
The dry nature of a traditional sauna is not continuous, as moisture can be temporarily introduced through a practice known as löyly (pronounced “low-loo”). This process involves carefully casting small amounts of water onto the superheated rocks atop the sauna stove. The water instantly turns into a burst of steam, which is the löyly.
The introduction of löyly causes a momentary spike in the room’s humidity, which can temporarily rise to between 40% and 60%. This sudden increase in moisture dramatically changes the sensation of the heat. The steam reduces the body’s ability to cool itself through sweat evaporation, making the air feel hotter than the thermometer indicates.
The resulting wave of heat is a brief, controlled event, often lasting less than a minute before the air begins to dry out again. This temporary moist heat is described as a softer, more enveloping warmth compared to the harshness of the dry, high-temperature air. The practice intensifies the session and creates a powerful, transient wave of heat that deepens the experience.
Differentiating Saunas from Steam Rooms
The distinction between a sauna and a steam room is defined by their approach to temperature and humidity. While a sauna begins dry and uses löyly to introduce temporary moisture, a steam room maintains maximum humidity constantly. Steam rooms, sometimes called Turkish baths, operate at a much lower air temperature, typically between 110°F and 120°F (43°C and 49°C).
These environments are saturated with moisture, achieving a relative humidity level of near 100%. The continuous, high humidity is generated by a wet heat source, such as a steam generator, which constantly injects vapor into the room. This saturated air prevents cooling through sweat evaporation, making the lower temperature feel intense.
The goal of a steam room is to create a dense, tropical-like atmosphere that is fundamentally different from the dry, high-temperature conditions of a traditional sauna. The constant 100% humidity is the defining characteristic of a steam room. In contrast, the ability to control the moisture level—from dry baseline to temporary steam burst—is the hallmark of a sauna.