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Heat Stroke & Heat Exhaustion: Signs, Symptoms and First Aid

When temperatures rise or during heat waves, our bodies can struggle to stay cool, leading to serious heat-related emergencies such as heat exhaustion and heat stroke. These conditions could get out of hand and turn into a real threat to life if not treated right away.

Understanding the signs and knowing how to respond can make all the difference in keeping yourself and others safe during those hot days. Heat cramps, heat exhaustion, or heat stroke, can happen to anyone who stays in the summer heat and sun for too long. Stay alert, stay cool, and be prepared with these first aid tips.

What is heat exhaustion?

Heat exhaustion happens when your body starts to overheat, especially when you're sweating a lot and not getting enough fluids and electrolytes to replace what you've lost. It usually happens after you've been active for a long time in a hot place, especially if it's humid or there's not much airflow, because that makes it tough for sweat to evaporate.

This condition is a warning sign that your body's cooling systems are getting overwhelmed. As blood rushes to the skin to cool you down, less blood reaches your vital organs, which can lead to mild shock. Keep an eye on the person, as heat exhaustion can turn into heat stroke if left untreated.

What is heat stroke?

Heat stroke is a life-threatening emergency where the body's cooling system is completely overwhelmed and can no longer cool itself. When this happens, you stop sweating because you're not drinking enough fluids. Without sweat, your body's temperature rises quickly. When it gets too high, your brain and other vital organs can start to shut down. The person becomes unresponsive, may have seizures, and requires immediate first aid.

Young children, older adults, those with chronic illnesses such as heart disease, and those taking certain medications can become ill in hot, humid weather faster than healthy adults.

It is important for everyone who enjoys the outdoors to know how to prevent heat emergencies, recognize when someone has been in the heat for too long, and provide help when needed.

Heat stroke vs heat exhaustion

Understanding the difference between heat exhaustion and heat stroke is super important:

  • Heat exhaustion is an early warning sign. The body is struggling to cool itself but is still mostly functioning.
  • Heat stroke is a life-threatening emergency where the body's cooling system fails completely.

Key differences:

  • Heat exhaustion symptoms: sweating, weakness, dizziness
  • Heat stroke symptoms: hot, dry skin, confusion, possible loss of responsiveness.

Without treatment, heat exhaustion can quickly progress to heat stroke.

Signs and symptoms of heat exhaustion

Based on the Canadian Red Cross First Aid Standards, the heat exhaustion symptoms are:

  • Moist, warm skin
  • Headache
  • Weakness or exhaustion
  • Nausea or vomiting
  • Dizziness or fainting
  • Anxiety

The signs and symptoms of heat exhaustion listed in bold in the list above are the most serious. Call 911 or your local emergency number immediately if any of these are present. Otherwise, provide care and monitor the person closely.

Signs and symptoms of heat stroke

Some of the signs of heat stroke are:

  • Hot, dry skin
  • Severe headache
  • Unresponsive
  • Seizures
  • Altered behaviour (bizarre, irritable, aggressive)
  • Rapid, shallow breathing
  • Rapid, irregular, weak pulse

Heat stroke is the least common but most severe heat-related illness, according to the Canadian Red Cross First Aid Standards. It is a life-threatening emergency, so call 911 or your local emergency number immediately if you suspect someone is experiencing heat stroke.

Learn how to recognize heat stroke manifestations and respond to heat emergencies in real-life scenarios. Explore Wilderness & Remote First Aid training.

How to help

When you’re hot, you sweat more than normal, so you need to drink more to replace the water your body is losing. Drink plenty of cool fluids, even if you do not feel thirsty, but avoid caffeine and alcohol. They can cause dehydration, which can prevent your body from regulating its temperature properly.

How to treat heat exhaustion

Call 911 or your local emergency number if the person is nauseous, vomiting, dizzy, anxious, has an altered level of responsiveness, or is unable to drink fluids.

Provide care following these steps:

  1. Get the person out of the heat and into some shade or a cool place, if you can.
  2. Loosen up any tight clothes and take off any heavy gear.
  3. Splash some cool water on their clothes or damp some towels and put them on their chest. Use a fan for extra cooling, but don't dry their skin.
  4. Place ice or cold packs under their armpits and on their chest.  
  5. If they're awake and able to drink, let them sip a cool drink with electrolytes, such as sports drinks, coconut water, juice, or even milk. If none of that's around, just give them some water.
  6. Make sure they take it easy and avoid any more heat activities for the rest of the day.

How long does heat exhaustion last? Symptoms typically improve within 30 to 60 minutes of cooling down and rehydrating. Still, severe cases may take 1 to 2 weeks for full recovery.

How to treat heat stroke

If you think someone is having a heat stroke, call 911 or your local emergency number or ask someone else to call them and get an AED. While you are on the call, provide care with these steps:

  1. Move the person to a cooler environment.
  2. Lose any tight clothing and remove any padded clothing or equipment.
  3. Quickly lower the person's core temperature with as many of these methods as possible (in order of preference):
    • Immerse the person's forearms and hands in cool water.
    • Pour cool water onto the person's clothing and/or towels or clothes and place them on the person's chest. Fan the person to increase evaporation. Do not dry the person's skin.
    • Apply ice or cold packs to the person's armpits and chest.
  4. Keep using the quick-cooling methods mentioned earlier until the person's condition improves or emergency personnel arrive.
  5. If the person is responsive and able to swallow, have them slowly sip a cool electrolyte-replacement beverage (e.g., a commercial sports drink, coconut water, fruit juice, or milk). If a drink with electrolytes is not available, give the person water.

If the person is unresponsive and their breathing is not normal at any point while you are providing care, start CPR. Learn when and how to use compression-only CPR.

How long does heat stroke last? Initial symptoms can improve within 1 to 2 days. However, full recovery may take several weeks or even months, depending on the severity of organ damage and the individual's age and overall health. It's essential to learn first aid skills to respond effectively to this type of emergency; consider enrolling in our First Aid training courses.

Wilderness considerations

In remote areas, dealing with heat emergencies can be riskier since it takes longer to get help.

For example, a hiker exposed to direct sunlight for several hours without hydration may begin to show signs of heat exhaustion. If you don’t act fast, this can quickly become heat stroke.

If you are in a wilderness setting:

  • Prioritize early cooling and hydration
  • Plan evacuation if symptoms worsen
  • Monitor closely, as help may be hours away

Heat-related emergencies and other environmental illnesses can escalate quickly, especially in remote environments where help may be hours away. Register for a Wilderness & Remote First Aid course today and build the skills to respond with confidence.

How to prevent heat-related emergencies

  • Drink plenty of cool fluids, aiming for 8 glasses (250 mL each) daily, and more when active.
  • Avoid being outside during the hottest part of the day.
  • Check the humidex to understand how hot it really feels.
  • Wear light, loose clothing for better air circulation. A hat for the sun.
  • Use sunscreen (SPF 15 or higher) as sunburned skin reduces the body’s ability to cool itself.
  • Slow down your activities as it gets hotter and don’t work, exercise, or play for too long at a time.
  • Keep up with cardiovascular fitness.
  • Take a lot of breaks in a cool or shady area to let your body cool off. This will help if you do need to be outside when it’s really hot.
  • Gradually acclimate yourself to heat exposure before major activities.
  • Adjust work/rest cycles on hot days or during heat waves, plan outdoor activities for cooler times.
  • Choose water or juice for hydration instead of alcohol.

Preparing for heat is just one part of staying safe outdoors, explore other environmental emergencies you should be ready for and how to prepare.

This content is reviewed by Canadian Red Cross First Aid experts and aligned with Canadian Red Cross First Aid guidelines. It is a helpful reference, but it is not a replacement for proper first aid training. You can sign up for a First Aid course nearby to learn more and prepare yourself. Also, download the Red Cross First Aid app to easily access life-saving tips and instructions.