What Is Heat-Related Illness?

Medically Reviewed by Sabrina Felson, MD on February 23, 2024
5 min read

When the weather’s hot, your chances of getting a heat-related illness go up. That’s because high heat and humidity make it harder to cool off through sweating. And without fast treatment, this can lead to serious health problems.

Heat-related illnesses are often grouped together as hyperthermia. Hyperthermia refers to any condition where your body is unable to properly maintain its temperature and handle heat.

Anyone can get a heat illness, but the risk is higher for:

Here are some common heat-related illnesses and ways to avoid them.

This is the most serious heat-related illness. It happens when your core temperature increases fast due to high heat and humidity.

Symptoms include:

Act fast and follow these steps if you think someone’s having a heat stroke:

  • Call 911.
  • Stay with the person until help arrives.
  • Move them to a cool, shaded area or indoors with air conditioning or a fan.
  • Take off their outer clothes.
  • If possible, cool them with cold water or an ice bath.
  • Place ice or cold, wet cloths against a few key body parts: their groin, armpits, neck, and head.

At the hospital, someone with heat stroke will get intravenous (IV) fluids to rehydrate them and replace sodium and potassium. They may also need drugs to control seizures or other complications. They’ll  likely be put on bed rest and monitored for 24 hours to several days. 

This can happen when you spend a long time in high temps and don’t get enough water or other hydrating drinks.

Symptoms include:

  • Headache
  • Nausea
  • Dizziness
  • Weakness
  • Feeling irritable
  • Thirst
  • Lots of sweating
  • Increased body temperature
  • Peeing less than usual

Follow these first-aid steps if you think someone has heat exhaustion:

  • Take them to a clinic or emergency room or call 911.
  • Stay with them until they get medical care.
  • Take them out of the heat.
  • Cool their head, face, and neck with cold water. Use cold compresses or, if available, a sink or bath.
  • Encourage them to sip cool water often.

This condition is tied to overheating along with lots of physical activity. It can lead to irregular heart rhythms and seizures. It can also cause kidney damage.

Some symptoms of rhabdomyolysis are:

  • Muscle cramps or pain
  • Unusually dark pee the color of tea
  • Weakness
  • Inability to do hard exercise

Some people don’t have symptoms.

If you think someone might have rhabdomyolysis:

  • Tell them to stop exercising.
  • Give them water or other hydrating liquids.
  • Get them medical care right away and ask the doctor or nurse to check them for rhabdomyolysis.

Dehydration or being unable to adjust to a new climate may play a role in this condition. Some symptoms are:

  • Fainting for a short time
  • Feeling dizzy
  • Being lightheaded after you’ve stood for a while, or after you suddenly get up from sitting or lying down

If you think someone has heat syncope, have them sit or lie down somewhere cool. Encourage them to take slow sips of water, clear juice, or a sports drink.

These usually strike when you’re exercising outdoors. You sweat so much that your muscles cramp up because you’re losing fluids and salts called electrolytes. Heat cramps can also be a sign that you have heat exhaustion.

Symptoms include muscle pain or cramping, and spasms in the belly, arms, or legs. To avoid or ease them:

  • Get out of the heat.
  • Sip water and have a snack or sports drink every 15 to 20 minutes.
  • Don’t take salt tablets.
  • Gently massage the cramping muscle.

Call a doctor if someone with heat cramps:

  • Has heart problems
  • Eats a low-sodium diet
  • Has cramps that don’t go away within an hour.

Your skin can get irritated when you sweat a lot during hot, humid weather. A heat rash looks like a red group of pimples or tiny blisters. Some places they tend to show up are:

Take these steps to help a heat rash go away:

  • Go somewhere cooler and less humid if possible.
  • Keep the affected area dry.
  • Apply powder to soothe it.
  • Don’t use ointments or creams.

Follow these tips to keep the heat away and stay hydrated:

Dress safely. Wear clothes that are lightweight, light-colored, and fit loosely.

Spend as much time indoors with air conditioning as you can. If you don’t have AC at home, call your local health department to find out if a heat-relief shelter is nearby. You could also consider going to an air-conditioned place like a public library or a mall. Also cut back on using your stove and oven to keep the home cooler. An electric fan can help, but it’s not enough. It’s better to take a cool bath or shower, or go somewhere with AC.

Limit outdoor activities. Save them for the morning and evening when it’s cooler. If you’re exercising or playing sports, take frequent breaks in the shade.

Exercise carefully. Stop right away if your heart pounds or you’re short of breath or feeling lightheaded. Go somewhere cool, rest, and hydrate.

Shield yourself from the sun. Before you go outside, put on broad-spectrum sunscreen with an SPF of at least 15. Also wear a hat and shades. Sunburn makes it harder for your body to cool down, and it can dehydrate you.

Protect your children and pets. Never leave them in a car, even with a window cracked open. They could have a heatstroke or die. When you get out of the car, make sure everyone’s with you.

Skip hot or heavy meals. They can boost your body heat.

Track the heat. Check your local news each day to find out if there are extreme heat alerts.

Get acclimated. If you’re starting a new job or other activity that requires you to exert yourself in hot conditions, expose yourself to the heat gradually over 2 or 3 days so your body can get used to it.

Drink more. When it’s hot out, drink more water or other liquids than usual, even if you’re not very active. That said, ask your doctor how much you should drink if you take water pills or if they’ve put a limit on your fluid intake due to a health condition.

Sip smart.Stick to water and other thirst-quenchers. Cut back sugary or alcoholic drinks -- they can lead to loss of fluids. Also skip very cold drinks. These can give you stomach cramps. And don’t forget your pet.Make sure they have lots of fresh water in a shady part of your home. Talk to your doctor before you have a sports drink if you follow a low-salt diet or have diabetes, high blood pressure, or other health conditions.