It was a balmy day on the North Carolina beach, the kind where you felt like you could lie on the warm sand for hours. That’s exactly what my friend’s brother Bill (not his real name) did after a long swim in the ocean.

Bill was a lumberjack and glad to be on vacation. Although badly sunburned, he was in unusually high spirits, almost giddy. Maybe that’s why, after he joined us at a picnic table in the shade, I wasn’t startled when he suddenly threw himself backwards off the bench. He was a bit of a prankster, and for a long moment I sat transfixed, waiting for him to explain the joke. Then there were shouts and screams from his family, and I realized something was horribly wrong.

Jumping up, I saw Bill in convulsions on the ground. His young sister, a registered nurse, ran to his side. It’s heat stroke, she called over her shoulder, securing his tongue so he wouldn’t swallow it. Her hands shaking, she loosened Bill’s shirt and used water-soaked napkins to cool him as her parents helped load him into the car to race to the closest emergency room.

It was my first experience with heatstroke, a life-threatening medical emergency. It’s an illness that’s usually preceded by heat exhaustion, a condition marked by heavy sweating and a rapid pulse. We had missed the earlier signs — I had even noticed that Bill was sweating profusely on the beach, but didn’t think anything of it. Even his giddiness was a sign of heat illness.

What caused the heat stroke? Too much heat and humidity and the long swim, probably combined with drinking too little water, we learned later. Bill’s sunburn also made it harder for his body to relieve the heat.

Exposure to high temperatures, especially if it’s humid, combined with vigorous physical activity are the usual culprits in heat illnesses. It’s not necessary to exercise to fall ill, though. Many older people have gotten heatstroke while sitting in sweltering houses during a heat wave; young children are also especially vulnerable.

In addition, many medications, including certain antihistamines, beta blockers, diuretics and psychiatric medicines (as well as alcohol and recreational drugs) can make you more susceptible to heat exhaustion.

Related: 7 Signs You Need a Drink (of Water!)

When your body is overwhelmed and can no longer cool itself off by sweating, your core temperature rises. If it gets too high, you can develop heat stroke.

Signs and symptoms of heat exhaustion

Heat exhaustion is usually preceded by heat cramps, the mildest heat syndrome. Here are heat exhaustion red flags:

  • Profuse sweating
  • Weakness
  • Weak, rapid pulse
  • Muscle cramps
  • Nausea
  • Vomiting
  • Headache
  • Cool or moist skin with goosebumps, even though it’s hot
  • Lightheadedness
  • Dizziness or low pressure when standing
  • Fainting

First aid for heat exhaustion

It’s usually safe to treat heat exhaustion yourself. Here’s what to do:

  • Get the person to a cool, shady site.
  • Loosen tight clothing.
  • Give the person cool water (without ice), and follow that with a weak salt solution (1 teaspoon of salt in 1 quart of water) or a drink containing electrolytes, such as Gatorade or Pedialyte.(This assumes the victim is alert and able to swallow.)
  • Have the person lie down and elevate the legs and feet.
  • Give the victim a sponge bath or pour cool water over him.
  • Take his temperature every few minutes. Continue cooling him until temperature has dropped to 101 or 102 degrees F. If it starts to rise again, repeat the cooling process.
  • If the condition does not improve within 30 minutes, call 911 or go to an emergency facility immediately. If he’s vomiting, seems confused, has trouble breathing and has red, dry skin, seek emergency treatment right away.

Related: Dogs in Hot Cars: A Deadly Combination

Signs and symptoms of heat stroke

If you're playing, exercising, working or even just sitting in a hot house during scorching weather without drinking enough water or other fluids, your body may no longer produce enough sweat to cool itself. If so, you may stop sweating entirely and become confused, giddy, and lethargic. Your body temperature can climb over 106 degrees F (41 C), and you may get heat stroke, which can lead to coma and even death unless you get emergency medical attention.

Heat stroke is a medical emergency. Watch for these clues:

  • High body temperature, 103 degrees F or higher
  • Red, hot, flushed or dry skin
  • Rapid or shallow breathing
  • Confusion
  • Dark urine (a sign of dehydration)
  • Racing pulse
  • Hallucinations or disorientation
  • Unusual behavior, such as irritability or aggressiveness
  • Nausea
  • Throbbing or severe headache
  • Unconsciousness
  • Seizures or twitching

First aid for heat stroke

If you suspect someone has heat stroke:

  • Call 911 or get the person to an emergency room right away.
  • If you’re waiting for an ambulance, move to a shady area or air conditioning if possible
  • Quickly take off the outer layers of clothing.
  • Cool the victim immediately by spraying him with a garden hose, sponging him with cool water or wrapping him in cool, wet sheets and fanning him.
  • Put cold compresses or ice packs under his armpits and on the neck and groin.
  • Check the person’s body temperature using a thermometer. Continue cooling him until his temperature has dropped to 101 or 102 degrees F. (Keep checking every few minutes to make sure that it doesn't climb back up again; if so, resume the cooling treatment.)
  • Avoid giving the victim a beer or another alcoholic drink, even if it's cool. Ditto for cold tea or coffee.
  • Do not give the victim antihistamines or pain relievers such as aspirin.
  • If the ambulance is delayed, call the emergency room and ask what to do.

Preventing heat illness

The best way to escape heat exhaustion or worse on hot days includes using sunscreen to avoid sunburn, drinking plenty of (non-alcoholic) fluids, wearing loose, light-colored clothing (dark clothing absorbs heat), cooling off in the shade or air conditioning and avoiding hot cars. Check with your pharmacist to see which medicines may increase your risk of heat illness. 

During a heat wave or summer power outage, check on elderly friends and neighbors and get them to a cooling center if necessary.

We were lucky that day at the beach. The quick thinking by Bill’s sister (along with her medical training and the treatment in the ER) may have saved his life. Bill rejoined the vacation party several days later, grateful to emerge unscathed but a bit subdued. He was careful to stay in the shade.

Related: Heatstroke in Dogs and How to Avoid It

Diana is an award-winning writer and editor with more than 20 years' experience in magazine, video, book and digital journalism, with a specialty in health coverage. She was a longtime writer and news editor at the Center for Investigative Reporting; has written for publications from the Washington Post to the Times of London syndicate; and has served as a senior and/or consulting editor at Time Inc. Health, Hippocrates, HealthDay News Service and Reporting on Health. She was also editor in chief of Consumer Health Interactive, a national health and medical web site, and has reported on finance for Blueshift Research and PBS Frontline. Before joining SafeBee, she was editor of Bioenergy Connection, a national magazine about bioenergy at UC Berkeley. Her favorite safety tip: Wear a bike helmet.