Preventing overheating comes down to managing three things: how much heat your body absorbs, how efficiently it can cool itself, and how quickly you replace lost fluids. In the U.S. alone, heat caused 1,600 deaths in 2021, and most of those were preventable. Whether you’re working outdoors, exercising, or just trying to survive a heat wave at home, the strategies below will keep your core temperature in a safe range.
How Your Body Cools Itself
Your brain acts as an internal thermostat. When it senses rising core temperature, it triggers two main responses: sweating and redirecting blood flow to the skin. During severe heat stress, your body can push up to 60% of its blood output to the skin surface, where heat radiates away. Sweat evaporating off your skin handles the rest. These two systems working together are remarkably effective, but they have hard limits. High humidity slows evaporation. Dehydration reduces the raw material for sweat. And certain health conditions or medications can quietly disable these cooling systems when you need them most.
Stay Ahead of Thirst With Fluids
Thirst is a lagging indicator. By the time you feel it, your body is already behind on fluids and your cooling capacity has dropped. OSHA recommends drinking one cup (8 ounces) of water every 15 to 20 minutes when you’re active in the heat, which works out to roughly 32 ounces per hour. There’s also a ceiling: no more than 48 ounces per hour. Drinking beyond that can dangerously dilute the sodium in your blood, a condition called hyponatremia that can become a medical emergency on its own.
If you’re sweating heavily for more than an hour, water alone won’t cut it. You’re losing salt and electrolytes along with fluid, so sports drinks or electrolyte mixes help maintain the balance your muscles and nerves depend on. A good habit is to start hydrating before you go outside, not after you’ve already been sweating for 30 minutes.
Know When Fans Stop Working
Electric fans are one of the most common cooling tools, but they stop helping and can actually make things worse once temperatures climb high enough. The WHO cautions that fans may not prevent heat illness above 95°F (35°C), and the EPA’s guideline is similar: don’t rely on fans when the heat index exceeds 99°F. In dry, extreme heat (above about 115°F), studies show fans worsen nearly every measure of heat stress because they’re essentially blowing hot-oven air across your skin, speeding up heat absorption rather than cooling.
Fans work by accelerating sweat evaporation. In humid conditions below those thresholds, they’re still useful. But if you’re in a heat wave with temperatures in the triple digits, air conditioning is the only reliable indoor option. If you don’t have AC at home, public cooling centers, libraries, and shopping malls are worth the trip.
Dress for Heat, Not Just Style
Fabric choice matters less than you might expect based on marketing claims. Research comparing cotton, polyester, and moisture-wicking blends during exercise has produced mixed results. One study found that a cotton-wool blend kept core temperatures slightly lower than pure cotton or polyester during cycling. Another found no significant difference in core temperature or comfort between cotton and polyester-blend shirts during high-intensity treadmill running. What does make a clear difference is permeability: impermeable or tightly woven materials trap heat significantly more than breathable fabrics.
The practical takeaway: choose loose-fitting, light-colored clothing made from any breathable fabric. Tight clothing restricts airflow across your skin, and dark colors absorb more solar radiation. A wide-brimmed hat reduces direct sun exposure to your head and neck, which is where a large portion of heat absorption occurs outdoors.
Time Your Exposure Wisely
Occupational safety guidelines use a measurement called the wet bulb globe temperature (WBGT), which factors in air temperature, humidity, wind, and sun exposure all at once. Under NIOSH guidelines, even acclimatized workers face high risk during heavy labor once the WBGT hits 78.8°F (26°C), a number that’s far lower than most people would guess. For someone not used to the heat, heavy work becomes risky at just 73.4°F (23°C) WBGT.
You don’t need a specialized thermometer to apply this principle. Schedule strenuous outdoor activity for early morning or evening when temperatures are lower. Take breaks in the shade every 15 to 20 minutes during peak heat. If you’re new to working or exercising in heat, your body needs 7 to 14 days of gradually increasing exposure to acclimatize. During that ramp-up period, you’re substantially more vulnerable.
People at Higher Risk
Aging quietly degrades the body’s cooling system. Sweat glands atrophy and lose sensitivity over time, producing less sweat per gland. In older women, the density of functional sweat glands also drops. The result is that adults over 65 can’t dissipate heat as effectively even when they feel fine and are doing everything right.
People with type 2 diabetes face a separate problem: their skin blood vessels don’t dilate as well in response to heat. Since redirecting blood to the skin is one of the body’s two primary cooling mechanisms, this impairment meaningfully raises the risk of heat illness.
Several common medications also interfere with temperature regulation. Diuretics (often prescribed for blood pressure) increase fluid loss. Antihistamines and many psychiatric medications, including antidepressants and antipsychotics, can reduce sweating. Beta-blockers and other cardiovascular drugs may blunt the heart’s ability to ramp up blood flow to the skin. Even over-the-counter allergy medications with anticholinergic properties (like diphenhydramine) can suppress sweat production. If you take any of these, extra hydration and limiting heat exposure become more important, not optional.
Recognizing Heat Exhaustion vs. Heat Stroke
Heat exhaustion is your body sounding an alarm. It shows up as heavy sweating, nausea, dizziness, headache, and weakness. Your body temperature may be elevated but your cooling system is still working. Moving to a cool place, drinking fluids, and resting will usually resolve it within an hour.
Heat stroke is the alarm failing. The body’s temperature control system shuts down, sweating often stops, and core temperature can rocket to 106°F or higher within 10 to 15 minutes. Symptoms include confusion, slurred speech, loss of consciousness, and hot, dry skin (though some people still sweat). Heat stroke is a life-threatening emergency. Call 911 immediately.
How to Cool Someone Down Fast
If someone is showing signs of heat stroke, the single most effective cooling method is cold water immersion, essentially getting the person into a tub or pool of cold water. Studies of heat stroke cases show cold water immersion cools the body at roughly 0.2°C per minute with a 100% survival rate across 274 documented cases. Ice water doesn’t cool meaningfully faster than plain cold water (around 14°C or 57°F), so don’t waste time finding ice if cold tap water is available.
When a tub isn’t available, wrapping the person in wet towels with airflow from a fan cools at about 0.12°C per minute. Dousing with tepid water while fanning achieves a similar rate of roughly 0.14°C per minute. These methods are slower than immersion but far better than doing nothing. Apply ice packs or cold wet cloths to the neck, armpits, and groin, where major blood vessels run close to the skin surface, while you wait for emergency medical help.
Building a Daily Prevention Routine
Prevention works best as a set of habits rather than a reaction to feeling overheated. Pre-hydrate before going outside. Check the heat index, not just the temperature, since humidity dramatically changes how dangerous a given temperature actually is. Wear a hat and light clothing. Plan outdoor work or exercise around the coolest parts of the day. Take breaks before you feel like you need them.
Keep cold water accessible at all times. If you’re supervising others, whether children, outdoor workers, or elderly family members, check on them regularly rather than waiting for them to report symptoms. People in the early stages of heat illness often don’t realize how impaired they already are, which is exactly what makes overheating so dangerous and so preventable.