How to Tell the Difference Between Heat Stress, Exhaustion, and Stroke

The terminology around heat injuries and illness is often confusing. As extreme heat warnings sweep the U.S., here is what you need to know about heat stress, heat exhaustion, and heat stroke.

A 90°F-day might be perfect for the beach. But once you start working your body, whether it’s mowing the lawn, going for a hike, or sprinting to catch the bus, your metabolism ramps up, burning fuel and raising your body’s core temperature. Your heart compensates by pumping blood away from your overheated organs to your skin, where dilating blood vessels can dissipate the heat with the help of evaporating sweat. If you are dehydrated and can no longer sweat, if it’s humid and the sweat can’t evaporate, or if it is simply too hot for human adaptation, the process breaks down, leading to heat injuries and illnesses.

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Heat Stress

Heat Stress is a catch-all phrase that generally refers to any negative outcomes from doing activity in the heat. Symptoms, from heat rash to cramps, dizzy spells, and fainting, are early warning signs that the body’s self-cooling mechanism is overwhelmed. If unaddressed, heat stress can lead to more severe consequences, such as heat exhaustion and heat stroke.

People suffering from heat stress should stop any activity, move to a cooler, shaded environment, and drink water or clear juice in slow sips. Cramps usually occur when the body has sweated too much, depleting water and electrolyte levels. Gatorade, Pedialyte, or other sports drinks can help replace lost fluids and electrolytes, but energy drinks should be avoided—the extra caffeine leads to greater dehydration. If the cramps do not subside within an hour, or the patient has heart problems or is on a low sodium diet, the U.S. Centers for Disease Control and Prevention recommends calling a medical professional.

Read more: How Extreme Heat Impacts Your Brain and Mental Health

Heat Exhaustion

When the body has lost too much water and electrolytes due to excessive sweating, heat exhaustion can set in. Symptoms can include nausea, vomiting, fainting, slurred speech, physical weakness, a bad headache, irritability, clammy skin, and an elevated body temperature. Repeated incidents of heat exhaustion can also lead to organ damage, particularly for the kidneys. Severe heat exhaustion can bring on rhabdomyolysis, a breakdown of muscle tissues that can cause irregular heart rhythms, seizures, and acute kidney damage.

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Victims of apparent heat exhaustion should be immediately moved to a cool—air conditioned if possible—area, and encouraged to take small, frequent sips of cool liquids. Call 911 if the person cannot be taken to a medical clinic or emergency room. Remove shoes, socks, and any restrictive or heavy clothing, and bathe the head, face, neck, and wrists with water or cold compresses.

Heat Stroke

Heat stroke is the most serious heat-related illness. It is triggered when the body is no longer capable of temperature regulation, and the core body temperature exceeds 104°F. The body will stop sweating as basic functions shut down, and core temperature can go as high as 108°F within 10-15 minutes. Other symptoms can include a loss of consciousness, seizures, or delirium. If the victim doesn’t receive immediate medical attention, which can include a cold IV drip, permanent disability or death is likely to come within a few hours.