Heat exhaustion vs. heat stroke: Signs and what to do

Heat-related illness exists on a spectrum, and where a person falls on that spectrum determines whether they need rest and fluids or an emergency response team. Heat exhaustion and heat stroke are not the same condition — one is a warning that the body's cooling system is being overwhelmed, and the other is a medical emergency in which the body's core temperature has reached a level that threatens the brain and organs. Knowing how to tell them apart, and how to respond, can be life-saving.

Choosing the right care setting matters when heat illness strikes. Our guide on urgent care vs. the ER helps you decide quickly — most heat exhaustion cases can be handled at urgent care, while heat stroke requires emergency services.

How heat-related illness develops

The human body regulates its core temperature primarily through sweating. As sweat evaporates, it cools the skin and draws heat away from the body's core. In hot environments — particularly with high humidity, which impairs sweat evaporation — this cooling mechanism can be overwhelmed. When the body can no longer keep up, core temperature begins to rise. Heat exhaustion is the intermediate stage. Heat stroke is the critical failure point.

Heat exhaustion: symptoms and what to do

Heat exhaustion occurs when the body is losing or has lost significant fluid and electrolytes through sweating. Core temperature is elevated but remains below 104°F (40°C). The brain and organs are not yet in danger, but the body is giving clear warning signs:

• Heavy sweating
• Cool, pale, clammy skin
• Fast but weak pulse
• Nausea or vomiting
• Muscle cramps
• Tiredness, weakness, and dizziness
• Headache
• Fainting or near-fainting

Importantly, a person with heat exhaustion is still mentally alert. They may feel terrible, but they know where they are and what's happening. If confusion or disorientation appears, the situation has escalated beyond heat exhaustion.

What to do for heat exhaustion: Move the person out of the heat immediately — into air conditioning if possible, otherwise shade. Have them lie down with their legs slightly elevated to improve circulation. Apply cool, wet cloths to the skin. Give cool water or an electrolyte drink in small sips if they are conscious and not vomiting. Do not give fluids to someone who is vomiting or unconscious. Seek medical care if symptoms don't improve within 30 minutes.

Heat stroke: symptoms and emergency response

Heat stroke occurs when core body temperature exceeds 104°F (40°C). At this temperature, the brain and organs are directly at risk. Untreated heat stroke can cause permanent organ damage, brain damage, or death. This is a 911 emergency — not an urgent care situation.

Two types of heat stroke exist: exertional heat stroke, which develops quickly during intense physical activity (typically in younger, healthy people), and classic heat stroke, which develops more slowly during prolonged heat exposure (more common in older adults and those with chronic illness).

The hallmark symptoms of heat stroke:

• Core temperature above 104°F
• Hot, red skin — may be dry (especially in classic heat stroke) or damp (more common in exertional heat stroke)
• Rapid and strong pulse
• Confusion, disorientation, agitation, or bizarre behavior
• Slurred speech
• Seizures
• Loss of consciousness

The critical distinguishing feature from heat exhaustion: mental status changes. A confused, disoriented, or unconscious person in a hot environment has heat stroke until proven otherwise. Act accordingly.

What to do for heat stroke: Call 911 immediately. While waiting for emergency services, move the person to a cool environment and begin aggressive cooling: immerse them in cold or ice water if possible, apply ice packs to the neck, armpits, and groin, and fan the skin with cool water misting if full immersion isn't available. Do not give the person fluids by mouth if they are confused or unconscious.

Key differences at a glance

• Sweating: Heat exhaustion — heavy sweating. Heat stroke (classic) — may stop sweating entirely.
• Skin: Heat exhaustion — cool, pale, clammy. Heat stroke — hot, red, dry or wet.
• Mental status: Heat exhaustion — alert. Heat stroke — confused, disoriented, or unconscious.
• Temperature: Heat exhaustion — elevated but below 104°F. Heat stroke — above 104°F.
• Action needed: Heat exhaustion — cooling, fluids, monitoring. Heat stroke — call 911 immediately.

Who is most at risk for heat-related illness?

Certain populations face higher risk from extreme heat. According to the CDC, these include older adults (especially those over 65), young children and infants, outdoor workers and athletes, people with chronic medical conditions including heart disease and diabetes, people taking certain medications (diuretics, antihistamines, antipsychotics, and beta-blockers can all impair the body's heat response), and people with limited access to air conditioning.

Prevention

Heat illness is largely preventable. During heat waves or periods of intense outdoor activity:

• Stay hydrated — drink water regularly, even before you feel thirsty
• Avoid alcohol and excessive caffeine, which promote dehydration
• Wear lightweight, light-colored, loose-fitting clothing
• Limit outdoor activity during peak heat hours (10 a.m.–4 p.m.)
• Never leave children or pets in a parked vehicle
• Check on elderly neighbors and relatives during heat events

When to visit urgent care

Heat-related illness often strikes when traveling. If you're away from home, our guide to navigating urgent care while on vacation covers what to expect and how to get care quickly.

Urgent care is appropriate for heat exhaustion when home measures aren't working — they can provide IV fluid rehydration and monitoring to help the body recover faster. If someone shows any signs of heat stroke (confusion, very high temperature, hot dry skin, loss of consciousness), skip urgent care and call 911. Time is critical. If you're unsure whether what you're seeing is heat exhaustion or heat stroke, treat it as heat stroke until emergency services arrive.