Summer Hydration Safety: Preventing Heat Exhaustion & Heatstroke

Summer heat is the most common cause of dehydration and the deadliest. Heat-related illness kills hundreds of people in the U.S. each year and sends thousands more to emergency rooms. The good news is that almost all heat-related illness is preventable with proper hydration and behavior. This guide covers how to recognize early warning signs, who is most at risk, and how to stay safe in extreme heat.

Understanding Heat-Related Illness

Heat-related illness exists on a spectrum from mild heat cramps to life-threatening heatstroke. Heat cramps are painful muscle spasms that occur during or after intense exercise in heat, caused by loss of sodium and fluid through sweating. They typically affect the legs, arms, or abdomen. Heat cramps can be treated by stopping activity, moving to a cool place, drinking water or a sports drink with electrolytes, and gently stretching the affected muscles.

Heat exhaustion is more serious and develops when the body loses significant fluid and electrolytes through prolonged sweating. Symptoms include heavy sweating, weakness, fatigue, dizziness, headache, nausea, muscle cramps, rapid pulse, and cool, moist skin with goosebumps despite the heat. Body temperature may rise to 38 to 40 degrees Celsius (100.4 to 104 degrees Fahrenheit). Heat exhaustion requires immediate treatment: move to a cool place, drink water or a sports drink, remove excess clothing, apply cool wet cloths or take a cool shower, and rest. If symptoms do not improve within an hour, seek medical attention.

Heatstroke is a medical emergency and occurs when the body's temperature regulation system fails completely. Body temperature rises above 40 degrees Celsius (104 degrees Fahrenheit), and the body stops sweating. Symptoms include hot, dry skin (or in some cases, still sweating), confusion, agitation, slurred speech, rapid pulse, nausea, vomiting, flushed skin, rapid breathing, and loss of consciousness. Heatstroke can damage the brain, heart, kidneys, and muscles, and can be fatal within hours if not treated. Call emergency services immediately and begin cooling the person with cold water, ice packs, or wet sheets while waiting for help.

Who Is Most at Risk?

Certain populations are at significantly higher risk of heat-related illness. Infants and young children cannot regulate their body temperature as efficiently as adults and depend on caregivers to manage their environment and fluid intake. Never leave a child in a parked car, even for a minute — interior temperatures can rise to dangerous levels within minutes, and dozens of children die in hot cars each year. Older adults have reduced thirst sensation, less efficient sweating, and often take medications that affect fluid balance.

People with chronic medical conditions — particularly heart disease, kidney disease, diabetes, and lung disease — are at higher risk because their bodies are less able to cope with heat stress. Certain medications, including diuretics, beta-blockers, antihistamines, antidepressants, and some antipsychotics, impair the body's ability to regulate temperature or increase fluid loss. Athletes who train intensely in heat, outdoor workers (construction, agriculture, landscaping), and pregnant women are also at elevated risk.

Socioeconomic factors also play a role. People who cannot afford air conditioning, who live in urban heat islands (neighborhoods with lots of concrete and little green space), or who work outdoors for a living face disproportionate heat exposure. Community-level interventions — cooling centers, tree planting, accessible public pools — are important public health measures for protecting vulnerable populations during heat waves.

Hydration Strategies for Hot Weather

In hot weather, your daily water needs increase significantly. Calculate your baseline with our Daily Water Intake Calculator, then add 500 to 1,000 ml per hour of outdoor activity. Drink before you feel thirsty — in heat, thirst is a late signal that dehydration has already begun. Carry a water bottle everywhere and sip continuously rather than gulping large amounts infrequently.

For activity lasting more than an hour in heat, choose a sports drink containing 6 to 8 percent carbohydrate and electrolytes (particularly sodium) over plain water. The sodium helps your body retain fluid and stimulates thirst, encouraging continued drinking. Avoid alcohol in heat — it impairs your body's ability to regulate temperature and increases urine output, accelerating dehydration. Caffeine in moderate amounts (1 to 2 cups of coffee) is fine and not significantly dehydrating for regular consumers.

Eat water-rich foods. Watermelon, cucumber, oranges, strawberries, and salads all contribute to hydration and provide electrolytes and other nutrients. Broth-based soups served cold (like gazpacho) are excellent summer hydration foods. Avoid heavy, salty, or greasy foods in extreme heat, as they increase thirst and can make you feel sluggish. For more food ideas, see our guide to 20 water-rich foods.

Beyond Hydration: Behavioral Strategies

Hydration alone cannot prevent heat illness if other factors are not managed. Schedule outdoor activities for early morning or evening when temperatures are lower. Avoid intense outdoor exercise between 10 AM and 4 PM on hot days. Wear loose, light-colored, breathable clothing that reflects heat and allows sweat to evaporate. A wide-brimmed hat and sunglasses protect against direct sun exposure.

Take frequent breaks in cool or air-conditioned spaces. If you do not have air conditioning at home, identify public cooling centers (libraries, malls, community centers) where you can go during the hottest part of the day. Use fans strategically — they help sweat evaporate, which cools the body, but they do not actually lower temperature and can be counterproductive above 32 degrees Celsius (90 degrees Fahrenheit) if they just circulate hot air. A cool shower or bath is more effective for rapid cooling.

Acclimatize gradually to heat. If you are not used to hot weather, limit outdoor activity for the first few days and gradually increase duration and intensity over 1 to 2 weeks. Heat acclimatization improves your body's ability to sweat and cool itself, but it takes time. Athletes training in heat should follow the same gradual progression. Pay attention to heat advisories and air quality alerts from local weather services, and adjust plans accordingly.

Recognizing Emergencies and Acting Quickly

The key to preventing heat tragedy is recognizing the warning signs and acting quickly. If you or someone near you shows signs of heat exhaustion — heavy sweating, weakness, dizziness, headache, nausea — stop activity, move to a cool place, drink fluids, and apply cool wet cloths. If symptoms do not improve within 30 to 60 minutes, or if they worsen, seek medical attention.

Signs of heatstroke — confusion, slurred speech, hot dry skin (or in some cases still sweating), loss of consciousness, body temperature above 40 degrees Celsius — require immediate emergency medical attention. Call emergency services, move the person to a cool place, remove excess clothing, and begin aggressive cooling with cold water, ice packs (especially at the neck, armpits, and groin), or wet sheets while waiting for help. Do not give fluids to someone who is confused or unconscious, as they may aspirate.

Check on neighbors, especially elderly or isolated individuals, during heat waves. Heat waves kill more people than any other weather event, and many victims live alone and are not discovered until it is too late. A simple phone call or visit can save a life. For more on recognizing dehydration signs, see our guide to the 12 signs of dehydration, and for exercise-specific guidance, see our hydration and exercise guide.