Preventing heat exhaustion comes down to managing three things: how much heat your body absorbs, how efficiently it can cool itself, and how well you replace what you lose through sweat. Most cases are entirely avoidable with the right preparation, but the specifics matter more than generic advice to “stay cool and drink water.”
Know the Early Warning Signs
Heat exhaustion announces itself before it becomes dangerous. The hallmark symptoms are heavy sweating, nausea, dizziness, headache, weakness, irritability, and a noticeable drop in urine output. Your body temperature rises but stays below the critical threshold. If you catch these signs and act on them, you recover quickly.
The danger is ignoring them. Heat exhaustion can progress to heat stroke, where the body’s cooling system fails entirely and core temperature can spike to 106°F or higher within 10 to 15 minutes. At that point, sweating often stops. The difference between the two isn’t subtle once you know what to look for: heat exhaustion means your body is struggling but still fighting. Heat stroke means it’s lost the fight.
Hydration Is More Than Water
Sweat rates during physical activity in hot conditions can reach 1 to 1.5 liters per hour for most people, and highly trained, acclimatized individuals can lose 2 to 3 liters per hour. That’s an enormous amount of fluid, and it carries significant amounts of sodium with it. Workers in moderate heat (around 95°F with 50% humidity) can lose 5 to 6 grams of sodium over a full shift, equivalent to 10 to 15 grams of table salt.
Plain water alone won’t replace what you’re losing. If you’re sweating heavily for more than an hour, you need a drink with meaningful sodium content. Most sports drinks are designed more for taste than for serious electrolyte replacement, so look for options with higher sodium or add a pinch of salt to what you’re drinking. Research on industrial fluid replacement suggests beverages should contain more than about 15 millimoles per liter of sodium, with minimal sugar. The practical takeaway: if you’re doing heavy outdoor work or prolonged exercise in the heat, water plus salty snacks or a proper electrolyte drink is far better than water alone.
Drink before you feel thirsty. Thirst is a lagging indicator, especially since some common medications actually blunt the thirst response.
Build Up Your Heat Tolerance Gradually
Your body can adapt remarkably well to heat, but it needs 7 to 14 days of gradually increasing exposure to get there. This process, called acclimatization, produces measurable changes: you start sweating sooner and more efficiently, you lose less sodium in your sweat, your heart rate stays lower at the same workload, and your core temperature stays more stable.
If you’re starting a new outdoor job, returning from vacation, or ramping up summer training, the first week is your highest-risk window. Start with shorter exposure times and lighter workloads, then build up over about two weeks. People who skip this step and jump straight into full-intensity work on a hot day account for a disproportionate share of heat illness cases.
Time Your Activity and Take Breaks
Environmental heat stress isn’t just about air temperature. Humidity, sun exposure, and wind all factor in. A measurement called Wet Bulb Globe Temperature (WBGT) captures all of these, and the thresholds it sets are worth knowing. Once WBGT exceeds about 80°F (roughly corresponding to a heat index well above 90°F in many conditions), even acclimatized people should limit activity and take rest breaks with water every 20 to 30 minutes. Above a WBGT of 88°F, everyone should avoid outdoor exertion and sun exposure entirely.
If you don’t have a WBGT reading, use common sense proxies. Schedule heavy outdoor work or exercise for early morning or evening. When you do work in peak heat, take breaks in shade before you feel like you need them. The length and frequency of those breaks should increase as the heat rises. Waiting until you feel exhausted to rest means you’ve already fallen behind on cooling.
Choose the Right Clothing
What you wear has a direct effect on your core temperature. In controlled exercise studies, synthetic moisture-wicking shirts resulted in significantly lower core body temperature compared to other fabrics, particularly as exercise duration increased. The synthetic fabric retained less sweat, allowing more of it to evaporate, and evaporation is your body’s primary cooling mechanism.
Loose-fitting, light-colored clothing works best. Tight clothing traps heat against the skin and limits airflow. Dark colors absorb more radiant heat from the sun. A wide-brimmed hat protects your head and face from direct solar radiation, which is one of the largest contributors to heat gain outdoors.
Use Active Cooling Strategies
When prevention alone isn’t enough, active cooling methods can meaningfully lower your body temperature. One of the most effective and practical options is consuming ice slurry, essentially a slushy. Drinking even a modest amount of ice slurry during breaks can drop core temperature by 0.4 to 0.7°C (roughly 0.7 to 1.3°F), and that cooling effect persists for 25 minutes or more after intake. That’s a bigger temperature reduction than drinking cold water alone.
Cold water immersion is also highly effective but requires dedicated facilities. More practical day-to-day options include wetting a bandana or towel with cold water and draping it around your neck, applying ice packs to pulse points (wrists, neck, inner elbows), and misting yourself with water in front of a fan. Cooling vests with ice inserts can help, though study results on their effectiveness during sustained activity are mixed.
Check Your Medications
Several common medication classes increase your vulnerability to heat in ways you might not expect. Diuretics (often prescribed for blood pressure) cause fluid loss and electrolyte imbalances. Antihistamines like diphenhydramine reduce sweating. Beta-blockers limit your blood vessels’ ability to dilate and release heat through the skin. Many psychiatric medications, including common antidepressants and antipsychotics, interfere with the brain’s temperature regulation or impair sweating.
Even over-the-counter pain relievers like ibuprofen and aspirin can play a role by affecting blood flow to the kidneys or reducing the dilation of blood vessels near the skin. If you take any of these medications regularly and spend time in the heat, you’re starting at a disadvantage. That doesn’t mean you need to stop your medications, but it does mean you should be more aggressive about every other prevention strategy on this list.
Protect Children and Older Adults
Children and adults over 75 face the highest risk of heat-related illness, but for different physiological reasons. Children have lower sweat rates and lower cardiac output than adults. They compensate by directing more blood flow to the skin to lose heat through direct contact with cooler air, but this strategy fails when air temperature approaches or exceeds skin temperature. In practical terms, children overheat faster than adults during the same activity in the same conditions, and they’re less likely to recognize or report early symptoms.
Older adults often have diminished sweat gland function, reduced cardiovascular capacity, and are more likely to be taking medications that impair thermoregulation. They also tend to have a blunted thirst sensation, making voluntary dehydration a quiet but serious risk. For both groups, the fix is the same: shorter exposure times, more frequent breaks, active prompting to drink fluids, and closer monitoring by someone who knows the warning signs. Don’t rely on a child or an elderly person to tell you they’re overheating. Watch for flushed skin, unusual fatigue, irritability, or confusion.