The important heat stroke signs and symptoms to look out for so you know when to give up on that run in the park and opt for the treadmill instead.


Whether you're playing ZogSports soccer or day drinking outside, heat stroke and heat exhaustion are a real danger. They can happen to anyone—and not just when temperatures hit the triple digits. What's more, passing out isn't the only sign of heat stroke. It might just be the climax to an already boiling-over situation. Luckily, there are ways to know when you're approaching dangerous territory so you can act fast and keep yourself safe this summer.

What Is Heat Stroke Exactly?

Understanding the difference between heat exhaustion and heat stroke is important because one precedes the other. Heat exhaustion, with its symptoms of nausea, excessive thirst, fatigue, weakened muscles, and clammy skin, will hit you first. If you don't pay attention to these heat exhaustion symptoms and act fast, you could be on your way to heat stroke. You do not want that.

"Any heat-related illness (HRI) can happen when the body exceeds its capacity to compensate for a rise in (internal) temperature," says Allen Towfigh, M.D., a neurologist and sleep medicine expert at the Weill Cornell Medical Center at New York–Presbyterian Hospital.

The breaking point varies from person to person, but "in healthy individuals, normal body temperature will cycle between 96.8 and 99.5 degrees Fahrenheit. However, with heat stroke we might see core temperatures of 104 degrees and higher," says Tom Schmicker, M.D., M.S., an orthopedic surgery resident at the Joan C. Edwards School of Medicine at Marshall University.

The effects can come on very quickly, reaching dangerous levels in just 15 to 20 minutes, often taking people by surprise, says Partha Nandi, M.D., F.A.C.P., a gastroenterologist in Detroit.

Here's what's happening: The brain (more specifically an area called the hypothalamus) is responsible for thermoregulation, explains Dr. Schmicker. "As body temperature rises, it stimulates sweating and diverts blood away from internal organs to the skin," he says.

Sweating is your body's main tool for cooling down. But unfortunately, it becomes less effective at high humidity levels-the sweat just sits on you rather than cooling you by evaporating. Other methods such as conduction (sitting on the cold floor) and convection (letting a fan blow on you) aren't enough to combat exceedingly high temperatures, he explains. With no defense against the rising temps, your body overheats, leading to heat exhaustion and potentially heat stroke.

Risk Factors for Heat Exhaustion and Heat Stroke

Certain conditions might put you at greater risk of heat exhaustion, and subsequently heat stroke. These include obvious environmental conditions (high temperatures and high humidity levels), dehydration, age (infants and the elderly), and physical exertion, says Dr. Towfigh. What's more, certain chronic medical conditions can put you at greater risk. These might include heart complications, lung disease, or obesity, as well as some medications, such as blood pressure medications, antidepressants, stimulants, and diuretics, says Minisha Sood, M.D., F.A.C.E., an endocrinologist at Fifth Avenue Endocrinology in NYC.

As for physical exertion, think about how heated you get doing burpees in an air-conditioned gym. It makes sense that doing the same exercise or something more intense outdoors under the sun can be even more taxing on your body as it tries to regulate the heat.

It's not just the heat alone, but rather the level of exertion and humidity combined, says Dr. Towfigh. A boot-camp workout in the park is clearly going to cause higher body temperature than say, a brisk walk or some push-ups in the shade. It's important to note, however, that there are always exceptions, particularly if you have any additional risk factors. So pay attention to whether you have any symptoms, whether you're in the shade or in the sun.

If you know the warning signs of heat stroke, you can prevent or avert it this summer and still enjoy your hikes, runs, and rides outside.

The Signs of Heat Stroke

Heat-related illness can happen to anyone. A few early but telling signs that something is wrong, says Dr. Towfigh, are flushed skin, lightheadedness, blurred vision, headache, tunnel vision/dizziness, and muscle weakness. These typically indicate heat exhaustion. But if it escalates (more on what to do immediately, below) you might also experience vomiting, slurred speech, and rapid breathing, says Dr. Sood. If left untreated, you could even experience a seizure or coma.

"As the body attempts to dissipate the heat, the blood vessels near the skin, called capillaries, dilate and the skin becomes flush," says Dr. Towfigh. Unfortunately, this can interfere with sufficient blood flow to the muscles, heart, and brain, he adds, as the body is directing blood flow toward the skin in an effort to regulate internal body heat.

"Unless heat stroke is treated quickly, it can result in potentially irreversible brain and organ damage, or even death," says Neha Raukar, M.D., associate professor of emergency medicine at Brown University. While these severe cases are rare, heat stroke-related brain damage can result in difficulty in processing information, memory loss, and attention deficits, she adds.

What You Can Do to Prevent and Treat Heat Exhaustion and Heat Stroke

Prevent It

A few ways to brace yourself against the heat:

  • Drink lots of fluids, but steer clear of alcohol, sugary drinks, and caffeine, says Dr. Nandi, as these have dehydrating effects. Rehydrate every 15 to 20 minutes if you're active outdoors, even if you don't feel thirsty, he says. Have a sports drink on hand to replace sodium and other minerals lost through sweat.
  • Take breaks when working out-you'll likely need intermittent recovery more often than you do during a typical indoor workout.
  • Dress appropriately in well-ventilated clothing.
  • Listen to your body. If you're mid-workout, but are feeling faint or extra clammy, it's smart to hit pause and step into the shade.
  • Choose a workout that works well with the weather. Instead of a run or bike ride, try grabbing a shady area in the park for some low-intensity yoga flows. You'll still reap the mental health benefits of spending time outdoors, but avoid the dangers of excess heat.

Treat It

If you experience any of the warning signs outlined above, or just feel too hot, take these steps:

  • Take off excess layers and change out of any clingy sweaty clothes.
  • If you're outside, hop into the shade ASAP. Apply a cold water bottle (or the water itself) to your pulse points, such as behind your neck and knees, under your arms, or near the groin. If you're near home or a park building with bathrooms, grab a cold, wet towel or compress and do the same.

If these methods aren't working and symptoms don't subside within 15 minutes, it's time to have someone take you to the emergency room.

Bottom line: Don't ignore your symptoms. Listen to your body. It takes just minutes for heat exhaustion to turn into heat stroke, which can do substantial permanent damage. No long run is worth that.