Dehydration: How to Prevent Heat Exhaustion and Heatstroke

By Drew Maffett
Current Master’s Degree Student, Sports and Health Sciences

The Fourth of July is right around the corner, which means everyone will be spending more time outside in the heat. Whether you’re grilling a meal, hiking, spending the day at the beach, or watching fireworks, it’s a good time to refresh your memory on dehydration symptoms and heat-related illnesses.

Dehydration occurs when your body loses more fluids than it takes in, making it harder to regulate your temperature, maintain blood pressure, and support normal body functions. While mild dehydration is common, it can quickly become dangerous, especially during hot weather or prolonged physical activity.

Common causes of dehydration include:

Excessive sweating
Vomiting
Diarrhea
Fever
Strenuous exercise
Certain medications
Lack of enough fluids, especially water

Many people think dehydration happens suddenly, but it usually develops in stages. Dehydration can progress from heat cramps to heat exhaustion and heatstroke.

If you’re under the impression that dehydration isn’t a big deal, consider that even the FIFA World Cup mandates hydration breaks for players, especially during matches held in high temperatures. FIFA players are some of the fittest athletes in the world, but they need scheduled opportunities to cool down and replace lost fluids like everyone else.

What’s the Difference Between Heat Cramps, Heat Exhaustion and Heatstroke?

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Understanding the difference between various heat-related conditions can help you know when someone simply needs fluids or when they need emergency medical care.

Heat Cramps

Heat cramps are usually the first warning sign that your body is losing too much fluid and electrolytes through sweating.

Common symptoms include:

Painful muscle cramps or spasms (usually in the legs, arms or abdomen)
Heavy sweating
Intense thirst
Normal body temperature

Heat Exhaustion

Heat exhaustion develops when prolonged dehydration and continued heat exposure overwhelm your body’s ability to cool itself.

The signs of heat exhaustion are:

Headache
Dizziness
Nausea or vomiting
Fatigue and weakness
Dry mouth or dry lips
Dark yellow urine
Decreased urination
Excessive sweating
Cool, pale, clammy skin
Rapid heartbeat
Muscle cramps

Without treatment, heat exhaustion can progress to heatstroke.

Heatstroke

Heat stroke occurs when you are severely dehydrated. The body’s temperature regulation system fails, and the core body temperature reaches a temperature 104°F (40°C) or higher. Heatstroke is a medical emergency, and you should get medical help by calling 911 immediately.

The symptoms of heatstroke include:

Confusion
Slurred speech
Loss of consciousness
Seizures
Hot skin (the skin may be dry or still sweating)
Rapid heartbeat
High body temperature (104°F or higher)

Not every heat-related illness is treated the same way.

With heat exhaustion, your body can still regulate its core temperature, but it needs help. That’s why passive cooling is recommended.

Moving to a cool environment, drinking fluids, removing excess clothing, and applying cool towels allow your body’s natural cooling mechanisms to recover. Using aggressive cooling at this stage usually isn’t necessary and may be uncomfortable.

Heatstroke is different. Once someone develops heatstroke, the body’s temperature regulation system has failed. The person’s core temperature continues to rise, which can quickly damage the brain, heart, kidneys, and other organs.

In this situation, every minute counts. Rapid active cooling – such as applying ice packs to the neck, armpits, and groin or ice-water immersion if possible – should begin immediately while someone calls 911.

Using the wrong approach can delay lifesaving treatment. If someone with heatstroke receives only passive cooling, their body temperature may not decrease fast enough. That increases the risk of permanent organ damage or death.

Passive Cooling and Treating Heat Exhaustion

Passive cooling helps lower body temperature gradually. Some passive cooling techniques include getting the affected person to:

Move into a shady area or to an air-conditioned environment
Remove excess clothing
Drink water or oral rehydration solutions
Put on cool towels
Rest

Active Cooling and Treating Heatstroke

Heatstroke requires rapid, active cooling while emergency medical services are on the way.

Some active cooling treatments include:

Ice-water immersion if available
Ice packs on the neck, armpits, and groin
Cold water with continuous fanning

When Is Urgent Care Appropriate?

Not every case of dehydration requires an emergency room visit, but some symptoms should be evaluated by a healthcare provider as soon as possible.

Consider visiting an urgent care center if you:

Continue vomiting and can’t keep fluids down
Feel dizzy or lightheaded even after drinking fluids
Notice persistent dehydration symptoms despite resting and rehydrating
Have signs of moderate dehydration, such as very dark urine or urinating much less than usual

Go directly to the emergency department or call 911 if you develop symptoms of severe dehydration or heatstroke.

How to Stay Hydrated

A good way to prevent dehydration is to stay ahead of your thirst. Here are some tips for staying hydrated:

Drink water consistently throughout the day, instead of waiting until you’re thirsty.
Increase your water intake during exercise and hot weather.
Replace electrolytes during prolonged sweating.
Choose drinks containing sodium, potassium and magnesium after long periods of activity.
Eat hydrating foods like watermelon, oranges, cucumbers and berries.
Limit excessive alcohol and caffeinated drinks, which can worsen fluid loss.

How Much Water Do You Need to Avoid Dehydration?

There isn’t a single universal number since hydration needs depend on body size, activity level, environment, and health status.

A common fluid intake for healthy adults is about 2-3 liters (11-15 cups) of fluids daily. This intake includes fluids from water, other beverages, and moisture-rich foods.

Your hydration needs increase significantly if you are:

Exercising or sweating heavily
Spending time in hot or humid environments
Experiencing vomiting, diarrhea or fever
Pregnant or breastfeeding

Rather than waiting until you’re thirsty (which can be a delayed signal) watch for early signs of dehydration, such as dark urine, dry mouth, fatigue, headache, or dizziness.

A simple, practical indicator is your urine color. Pale yellow generally suggests adequate hydration, while darker urine may indicate that you need more fluids.

In more severe cases, especially during illness or prolonged heat exposure, oral rehydration solutions or electrolyte-containing drinks may be more effective than water alone. They help replace both fluids and essential electrolytes that you lose lost through sweat or illness.

Special Populations and Dehydration

Certain populations are more vulnerable to dehydration, according to the Mayo Clinic. These populations include older adults, children and pregnant women, so remaining hydrated is vital.

Dehydration and Older Adults

Healthy aging brings changes that make dehydration easier to develop. As we age, the body’s fluid reserves decrease, kidney function becomes less efficient, and the sensation of thirst becomes less noticeable. Many older adults don’t realize they’re dehydrated until their symptoms have already progressed.

Certain medications, including diuretics (also known as “water pills”), along with illnesses like the flu or bladder infections, can also increase the risk of heat-related illnesses. Rather than relying on thirst alone, older adults should make drinking fluids a regular habit throughout the day, especially during hot weather.

Dehydration and Children

Children lose fluids more quickly than adults and often don’t recognize when they need to drink. Because of their smaller body size and higher percentage of body water, dehydration can develop much faster, especially during sports, outdoor play, or illnesses that involve vomiting and diarrhea.

Encourage frequent water breaks instead of waiting for children to ask for a drink. Watch for signs such as:

Dry mouth
Few or no tears when a child cries
Fewer wet diapers or trips to the bathroom
Sunken eyes
Unusual sleepiness
Irritability

Dehydration and Pregnant Women

Staying hydrated becomes even more important during pregnancy. Your body needs additional fluids to support increased blood volume, regulate your body temperature, and support your growing baby.

Dehydration can develop more quickly during hot weather, exercise, or illnesses that cause vomiting or diarrhea. Even mild dehydration can contribute to headaches, dizziness, fatigue, and overheating.

If you’re unable to keep fluids down or develop symptoms of severe dehydration, contact your healthcare provider promptly.

Set Yourself Up for Success – Build a Heat Kit!

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Heat-related illnesses are largely preventable. Recognizing the signs of dehydration, treating heat cramps early, and responding quickly to heat exhaustion can stop the body’s progression to heatstroke.

Make hydration part of your routine, not an afterthought. Starting a few simple habits today can help keep you and your family safe all summer long.

About the Author

Drew Maffett is an exercise physiologist and current graduate student at American Military University, where she is pursuing a master’s degree in sports and health sciences with a concentration in human performance. She holds a B.S. in exercise physiology from Ohio University and is a former U.S. Army combat medic.

Drawing on her background in military medicine and exercise physiology, Drew combines evidence-based science with clear communication to make health and performance topics accessible to all readers. She is passionate about reducing educational barriers and empowering people with the knowledge they need to make informed decisions about their health. Through her writing, Drew strives to translate complex scientific concepts into practical, engaging information that promotes curiosity, critical thinking, and lifelong learning.