How to Tell the Difference Between Heat Stroke and Heat Exhaustion

When Heat Becomes a Relentless Force

Summertime fun, a day of strenuous outdoor work, or a relentless heatwave can lead to the all-too-familiar feelings of being overheated. Most of the time, this leads to simple aches and cramps. But sometimes, the heat escalates, and your body’s natural cooling systems become overwhelmed. Knowing the difference between a warning sign and a full-blown emergency is not just helpful, it’s potentially life-saving.

We will walk you through the critical distinctions between heat exhaustion and heat stroke, reveal the three unmissable red flags that signal a crisis, and empower you with the simple yet powerful “Cool First” rule; a protocol that can make all the difference in a medical emergency.

The Heat Illness Spectrum

Heat-related illnesses exist on a spectrum, beginning with mild symptoms and escalating to life-threatening conditions. Understanding where a person falls on this spectrum is the first step toward effective intervention.

A. Heat Exhaustion

Heat exhaustion arises when the body overheats due to prolonged exposure to high temperatures or intense physical exertion without adequate hydration and cooling. This is your body’s alarm system, signaling that it is struggling to keep up.

• Physiology: Your body tries to cool itself through sweating and vasodilation; the widening of blood vessels near the skin’s surface to release heat. This process, however, can lead to significant fluid and electrolyte loss, causing dehydration and a drop in blood pressure.
• Symptoms: Core body temperature typically remains below 40°C (104°F). Common signs include heavy sweating, feeling weak, dizzy, nauseous, or a dull headache. The skin may feel cool and clammy. These symptoms are a clear warning to stop activity, find a cool place, and rehydrate.

B. Heat Stroke

Heat stroke is a medical emergency and the most severe form of heat illness. It occurs when the body’s primary cooling mechanism fails, leading to a dangerous rise in core body temperature and widespread organ damage.

• Physiology: At temperatures above 40°C (104°F), your body’s critical enzymes and cellular proteins begin to break down, leading to a systemic inflammatory response. This can cause vital organs, including the brain, liver, and kidneys, to fail. ^[2]

Types of Heat Stroke:

• Exertional Heat Stroke (EHS): Occurs in healthy, active individuals who are engaged in strenuous activity in hot or humid conditions.
• Non-Exertional Heat Stroke (NEHS): Affects vulnerable populations like older adults, infants, or people with chronic illnesses, often in the context of a prolonged heatwave without access to air conditioning.

When It’s a Life-Threatening Emergency

While heat exhaustion is manageable, heat stroke demands immediate, urgent intervention. The following three red flags are your cue to skip the rest and shade and go straight to emergency action.

1. Mental Status Changes and Confusion: This is the most critical red flag. The moment a person becomes disoriented, confused, irritable, or exhibits strange or irrational behavior, heat stroke has likely set in. Other signs include slurred speech, seizures, or loss of consciousness. The brain is highly sensitive to extreme heat, and neurological dysfunction is a clear sign of a thermoregulatory crisis. ^[4]
2. Absence of Sweating (Hot, Dry Skin): While heat exhaustion is characterized by heavy sweating, classic heat stroke (NEHS) often causes a complete cessation of sweat production. The skin will feel hot to the touch and dry. This is a sign that the body’s cooling system has shut down, and the core temperature is rising rapidly and unchecked. It is important to note that individuals with exertional heat stroke may still be sweating profusely, so this sign is not always present. ^[5]
3. Rapid Deterioration: The sudden progression of symptoms is a major red flag. If a person goes from feeling dizzy to becoming unconscious in a matter of minutes, or if their condition is not improving despite initial cooling efforts, it indicates that the illness is escalating and requires a higher level of care. Other signs of deterioration include a rapid, weak pulse; rapid, shallow breathing; or dark, concentrated urine, which signals dehydration and potential kidney damage.

The “Cool First” Rule

When you encounter someone with signs of heat stroke, the single best and safest rule is: Cool First, Then Call! Prioritize immediate cooling even before or while you are calling for emergency services. The goal is to lower the person’s body temperature as quickly as possible to prevent organ damage.

Immediate Cooling Measures

• Move to a Cooler Environment: Get the person out of the sun and into an air-conditioned space, a car with the AC on, or at the very least, a shaded area.
• Remove Excess Clothing: Take off any heavy or unnecessary clothing to allow heat to escape from the skin.
• Use Active Cooling: This is the most crucial step. Use a garden hose, a sponge, or spray bottle to apply cool water to the skin while fanning it vigorously. Place cold packs or cool, wet cloths on the neck, armpits, and groin; areas where major blood vessels are close to the surface.
• Ice-Water Immersion: For exertional heat stroke, ice-water immersion is the most rapid and effective method for cooling. Studies have shown that it can bring down a person’s core temperature far faster than other methods and is the gold standard for athletes and outdoor workers. ^[6]
• Hydrate (Only if Conscious and Not Vomiting): If the person is conscious and not vomiting, offer sips of ice-cold water or an electrolyte drink. Never give fluids to a person who is confused or unconscious, as they could aspirate the fluid into their lungs.

Why Speed is Critical

The “Cool First” rule is not just a catchy phrase; it’s an evidence-based medical protocol.

• Minutes Matter: Heat stroke can cause permanent organ damage within minutes. A high core body temperature can denature proteins and enzymes, leading to widespread cellular dysfunction. The longer the body remains hyperthermic, the greater the risk of long-term damage or death. ^[7]
• Stabilizing Vital Systems: Rapid cooling helps reverse the body’s systemic collapse. It helps stabilize enzymes, reduce the inflammatory response, and restore the function of vital organs like the kidneys, brain, and liver.
• Preventing Rhabdomyolysis: In exertional heat stroke, rapid cooling can help prevent rhabdomyolysis, a condition where muscle tissue breaks down and releases a protein into the bloodstream, which can lead to acute kidney failure.
• Improved Outcomes: Medical studies on exertional heat stroke have consistently shown that patients who receive immediate, aggressive cooling have a significantly lower mortality rate and better outcomes than those who do not. ^[9]

Stay Cool, Stay Safe

The best way to combat heat illness is to prevent it in the first place.

• Hydrate Proactively: Drink plenty of fluids, especially water or electrolyte drinks, throughout the day. Don’t wait until you feel thirsty; by then, you are already dehydrated.
• Time Your Activity: Avoid strenuous outdoor activities during the hottest hours of the day (usually 10 a.m. to 4 p.m.).
• Dress Appropriately: Wear loose-fitting, light-colored clothing made of breathable fabrics like cotton or linen.
• Acclimatize Gradually: If you are visiting a hot climate or starting a new outdoor job, gradually increase your exposure over a period of weeks to allow your body to adapt.
• Recognize Vulnerability: Be especially mindful of children, older adults, and those with chronic health conditions (e.g., heart disease, diabetes) who are more susceptible to heat-related illness. Also, be aware that certain medications can impair your body’s ability to cool itself.