Saunas, including traditional dry heat and lower-temperature infrared types, use controlled thermal exposure to induce deep sweating and temporarily increase heart rate. People seek this practice for benefits like relaxation, muscle recovery, and improved circulation. These effects occur because heat widens blood vessels, increasing blood flow to the skin as the body attempts to cool itself. While beneficial in moderation, prolonged exposure intensely challenges the body’s natural cooling mechanisms, quickly shifting the experience from therapeutic to hazardous.
Dehydration and Electrolyte Imbalance
The most immediate consequence of prolonged sauna use is excessive sweating, leading to significant fluid loss. A person can lose 0.5 to 1.0 liters of sweat in a typical 15- to 20-minute session, which directly reduces overall blood volume. When blood volume decreases, the heart must work harder to circulate the remaining fluid, causing the heart rate to increase significantly.
Sweat contains essential electrolytes, primarily sodium and chloride, necessary for nerve signaling and muscle function. Prolonged sweating without replacement causes an imbalance in these charged minerals. Loss of sodium can lead to muscle cramps, headaches, and fatigue. Drinking only plain water to replace this loss can dilute remaining electrolytes, a condition known as hyponatremia, complicating the body’s attempt to restore balance.
Recognizing Warning Signs and Immediate Action
The body provides distinct signals when the thermal stress threshold has been crossed, and recognizing these signs is imperative for safety. Symptoms of overexposure include intense dizziness or lightheadedness, often resulting from a heat-induced drop in blood pressure. Nausea, a sudden pounding headache, and the cessation of sweating are also common signs that core body temperature is rising too high.
If any warning signs appear, the immediate step is to exit the sauna at once. Find a cool place to lie down and gradually begin rehydrating with small, frequent sips of water or an electrolyte-containing beverage.
Hyperthermia and Severe Organ Stress
Staying in the heat past warning signs can quickly progress to hyperthermia, a dangerous elevation of core body temperature, often exceeding 104°F (40°C). This uncontrolled rise can lead to heat exhaustion and, most severely, heat stroke, a life-threatening medical emergency. Heat stroke occurs when the body’s temperature regulation system fails, marked by central nervous system dysfunction like confusion, delirium, seizures, or loss of consciousness.
Prolonged thermal stress places immense strain on the cardiovascular system, requiring the heart to significantly increase its rate and output for cooling. This rapid heart rate (tachycardia), coupled with low blood pressure (vasodilation), can strain the heart muscle and trigger an irregular heartbeat (arrhythmia). Severe hyperthermia can also cause widespread damage, including acute kidney injury, liver damage, and muscle tissue breakdown (rhabdomyolysis). Immediate, aggressive external cooling and professional medical intervention are necessary to reverse this condition.
Specific Populations at Increased Risk
Certain individuals face a significantly higher danger from prolonged sauna use due to compromised thermoregulation or existing health issues.
Cardiovascular Conditions
People with pre-existing cardiovascular conditions, such as unstable angina or recent myocardial infarction, are advised to avoid saunas altogether. The heat strain can severely aggravate these conditions.
Elderly and Pregnant Individuals
The elderly are at increased risk because their bodies have a reduced ability to regulate internal temperature, making them more susceptible to heatstroke. Pregnant individuals should exercise caution, as heat exposure carries a risk of overheating, fainting, and low blood pressure.
Alcohol and Medications
The consumption of alcohol before or during a session is particularly dangerous because it increases the risk of both dehydration and severe hypotension. This can lead to cardiac complications. Individuals taking certain medications, like diuretics or blood pressure drugs, must also consult a doctor. These drugs can interfere with the body’s ability to maintain fluid and electrolyte balance under heat stress.