A healthy body temperature is maintained by the nervous system. As the body temperature goes up, the body tries to stay at its normal temperature by transferring heat. Sweating and blood flow to the skin (thermoregulation) help us keep our bodies cool. A heat-related illness occurs when our bodies can no longer transfer enough heat to keep us cool.
A high body temperature (hyperthermia) can develop quickly in extremely hot environments, such as when a child is left in a car in the summer heat. Hot temperatures can also build up in small spaces where the ventilation is poor, such as attics or boiler rooms. People working in these areas may quickly get hyperthermia.
High temperature caused by a fever is different from a high body temperature caused by a heat-related illness. A fever is the body's normal reaction to infection and other conditions, both minor and serious. Heat-related illnesses produce a high body temperature because the body can't transfer heat as well as it should or because there's too much external heat gain.
Heat-related illnesses include:
Heat rash (prickly heat). It occurs when the sweat ducts to the skin become blocked or swell, causing discomfort and itching.
Heat cramps. They occur in muscles during and after exercise because sweating caused the body to lose water, salt, and minerals (electrolytes).
Heat edema (swelling) in the legs and hands. This can occur when you sit or stand for a long time in the heat.
Heat tetany (hyperventilation and heat stress). This is usually caused by short periods of stress in a hot environment.
Heat syncope (fainting). It's caused by low blood pressure when heat causes the blood vessels to expand (dilate). Then body fluids move into the legs because of gravity.
Heat exhaustion (heat prostration). It most often occurs when a person works or exercises in hot weather and doesn't drink enough liquids to replace those lost liquids.
Heatstroke (sunstroke). This occurs when the body doesn't regulate its own temperature. Body temperature keeps rising, often to 105°F (40.6°C) or higher. Heatstroke is a medical emergency. Even with immediate treatment, it can be life-threatening or cause serious long-term problems.
Often, environmental and physical conditions can make it hard to stay cool. Heat-related illness is often caused or made worse by dehydration and fatigue. Your risk goes up if you exercise during hot weather, work outdoors, and don't wear lightweight or loose-fitting clothing for the environment. Drinking alcohol also increases your risk of dehydration.
Many medicines increase your risk of a heat-related illness. Some medicines decrease the amount of blood pumped by the heart (cardiac output) and limit blood flow to the skin, so your body is less able to cool itself by sweating. Other medicines can change your sense of thirst or make your body produce more heat. If you take medicines regularly, ask your doctor for advice about hot-weather activity and your risk of getting a heat-related illness.
Other things that may increase your risk of a heat-related illness include:
Age. Babies don't lose heat quickly, and they don't sweat well. Older adults don't sweat easily. And they often have other health conditions that affect their ability to lose heat.
Obesity. People who are overweight have decreased blood flow to the skin. They hold heat in because of the insulating layer of fat tissue. And they have more body mass to cool.
Heat waves. People who live in cities are especially vulnerable to illness during a heat wave. Heat is trapped by tall buildings and air pollutants, especially if there's a high level of humidity.
Chronic diseases, such as diabetes, heart failure, and cancer. These conditions change the way the body gets rid of heat.
Travel to wilderness areas or foreign countries with high outdoor temperatures and humidity. When you go to a different climate, your body must get used to the differences (acclimate) to keep your body temperature in a normal range.
The medical assessment of symptoms is based on the body parts you have.
If you are transgender or nonbinary, choose the sex that matches the body parts (such as ovaries, testes, prostate, breasts, penis, or vagina) you now have in the area where you are having symptoms.
If your symptoms aren’t related to those organs, you can choose the gender you identify with.
If you have some organs of both sexes, you may need to go through this triage tool twice (once as "male" and once as "female"). This will make sure that the tool asks the right questions for you.
Did you pass out completely (lose consciousness)?
Yes
Lost consciousness
No
Lost consciousness
If you are answering for someone else: Is the person unconscious now?
(If you are answering this question for yourself, say no.)
Yes
Unconscious now
No
Unconscious now
Are you back to your normal level of alertness?
After passing out, it's normal to feel a little confused, weak, or lightheaded when you first wake up or come to. But unless something else is wrong, these symptoms should pass pretty quickly and you should soon feel about as awake and alert as you normally do.
Yes
Has returned to normal after loss of consciousness
No
Has returned to normal after loss of consciousness
Did the loss of consciousness occur during the past 24 hours?
Have you tried home treatment for more than 4 hours?
Home treatment includes resting, staying out of the heat and sun, using cool compresses or a fan to cool off, and drinking plenty of fluids.
Yes
Home treatment for more than 4 hours
No
Home treatment for more than 4 hours
Many things can affect how your body responds to a symptom and what kind of care you may need. These include:
Your age. Babies and older adults tend to get sicker quicker.
Your overall health. If you have a condition such as diabetes, HIV, cancer, or heart disease, you may need to pay closer attention to certain symptoms and seek care sooner.
Medicines you take. Certain medicines, such as blood thinners (anticoagulants), medicines that suppress the immune system like steroids or chemotherapy, herbal remedies, or supplements can cause symptoms or make them worse.
Recent health events, such as surgery or injury. These kinds of events can cause symptoms afterwards or make them more serious.
Your health habits and lifestyle, such as eating and exercise habits, smoking, alcohol or drug use, sexual history, and travel.
Try Home Treatment
You have answered all the questions. Based on your answers, you may be able to take care of this problem at home.
Try home treatment to relieve the symptoms.
Call your doctor if symptoms get worse or you have any concerns (for example, if symptoms are not getting better as you would expect). You may need care sooner.
Exposure to a hot environment can cause many problems. Problems can be mild, like a heat rash, swelling in the hands or feet, or heat cramps. But heat can also lead to more dangerous situations like confusion, seizures, or passing out.
Symptoms of heat exhaustion may include:
Weakness, dizziness, or fatigue.
Headache.
Nausea.
Skin that is pale, cool, and moist.
Raised body temperature.
Heat exhaustion may occur when you are sweating a lot (typically, while working or exercising in hot weather) and do not drink enough to replace the fluids you've lost.
Symptoms of difficulty breathing can range from mild to severe. For example:
You may feel a little out of breath but still be able to talk (mild difficulty breathing), or you may be so out of breath that you cannot talk at all (severe difficulty breathing).
It may be getting hard to breathe with activity (mild difficulty breathing), or you may have to work very hard to breathe even when you’re at rest (severe difficulty breathing).
Severe trouble breathing means:
You cannot talk at all.
You have to work very hard to breathe.
You feel like you can't get enough air.
You do not feel alert or cannot think clearly.
Moderate trouble breathing means:
It's hard to talk in full sentences.
It's hard to breathe with activity.
Mild trouble breathing means:
You feel a little out of breath but can still talk.
It's becoming hard to breathe with activity.
Severe trouble breathing means:
The child cannot eat or talk because he or she is breathing so hard.
The child's nostrils are flaring and the belly is moving in and out with every breath.
The child seems to be tiring out.
The child seems very sleepy or confused.
Moderate trouble breathing means:
The child is breathing a lot faster than usual.
The child has to take breaks from eating or talking to breathe.
The nostrils flare or the belly moves in and out at times when the child breathes.
Mild trouble breathing means:
The child is breathing a little faster than usual.
The child seems a little out of breath but can still eat or talk.
If you have symptoms of heat exhaustion, try the following first aid to cool off:
Stop what you are doing and rest.
Get out of the sun and heat.
Remove any extra clothing.
Spray or mist the body with cool water.
Use a fan if one is available.
Drink plenty of cool water or rehydration drinks.
Signs that heat exhaustion is becoming severe include:
Blurred vision.
Fast breathing and fast heart rate (more than 120 beats per minute when you are at rest).
Severe belly cramps.
Very heavy sweating (sweat is pouring off you and soaking through your clothes).
Some other symptoms of heat-related illness include:
Muscle twitching or spasms.
Muscles that feel hard and lumpy.
Sore muscles.
Symptoms of heatstroke may include:
Feeling or acting very confused, restless, or anxious.
Trouble breathing.
Sweating heavily, or not sweating at all (sweating may have stopped).
Skin that is red, hot, and dry, even in the armpits.
Passing out.
Seizure.
Nausea and vomiting.
Heatstroke occurs when the body can't control its own temperature and body temperature continues to rise.
Seek Care Now
Based on your answers, you may need care right away. The problem is likely to get worse without medical care.
Call your doctor now to discuss the symptoms and arrange for care.
If you cannot reach your doctor or you don't have one, seek care in the next hour.
You do not need to call an ambulance unless:
You cannot travel safely either by driving yourself or by having someone else drive you.
You are in an area where heavy traffic or other problems may slow you down.
Call 911 Now
Based on your answers, you need emergency care.
Call 911 or other emergency services now.
Sometimes people don't want to call 911. They may think that their symptoms aren't serious or that they can just get someone else to drive them. Or they might be concerned about the cost. But based on your answers, the safest and quickest way for you to get the care you need is to call 911 for medical transport to the hospital.
Seek Care Today
Based on your answers, you may need care soon.
Call your doctor today to discuss the symptoms and arrange for care.
If you cannot reach your doctor or you don't have one, seek care today.
If it is evening, watch the symptoms and seek care in the morning.
If the symptoms get worse, seek care sooner.
Try First Aid for Symptoms
Stop what you are doing and rest.
Get out of the sun and heat.
Remove any extra clothing.
Spray or mist the body with cool water.
Use a fan if one is available.
Drink plenty of cool water or rehydration drinks.
If your symptoms get better, you may not need to seek care today.
Apply ice packs over as much of the body as you can.
Do not use any medicine (such as aspirin, acetaminophen, or ibuprofen) to reduce the person's temperature.
Sometimes people don't want to call 911. They may think that their symptoms aren't serious or that they can just get someone else to drive them. Or they might be concerned about the cost. But based on your answers, the safest and quickest way for you to get the care you need is to call 911 for medical transport to the hospital.
Self-Care
Caring for a mild heat-related illness
Treating mild heat exhaustion
When recognized in the early stages, mild heat exhaustion can be treated at home.
Stop your activity.
Get out of direct sunlight. Lie down in a cooler environment, such as shade or an air-conditioned area. Prop up your feet. Take off all unneeded clothing.
Cool down by applying cool compresses or having a fan blow on you. Place ice bags under your arms and in your groin area.
Rest until you feel better. This may take a few days.
Treating other heat-related problems
Heat syncope (fainting) usually doesn't last long. It improves when you lie down in a flat position. It's helpful to lie down in a cooler environment.
Heat edema (swelling) is treated with rest and by raising the level of your legs. If you are standing for a long time in a hot environment, flex your leg muscles often. This can keep blood from pooling in your lower legs, which can lead to heat edema and fainting.
Heat cramps are treated by getting out of the heat and replacing fluids and salt.
If you aren't on a salt- (sodium-) restricted diet, eat a little more salt, such as a few nuts or pretzels. Do not use salt tablets. They are absorbed slowly and can irritate the stomach.
Try massaging and stretching your cramped muscles.
Heat rash (prickly heat) usually gets better and goes away without treatment.
Keep areas clean and dry to help prevent a skin infection.
Don't use baby powder while you have a rash. The powder can build up in the skin creases and hold moisture. This allows the growth of bacteria that may cause infection.
Dress in as few clothes as you can during hot weather.
Keep your home, especially sleeping areas, cool.
Acclimating to heat
Acclimation helps you remain active in a hot environment with less risk of a heat-related illness. You can acclimate yourself to a hot environment by gradually increasing the amount of time you exercise in the heat each day. Do this over 8 to 14 days. Adults usually need daily exercise periods that last 1 to 2 hours to become acclimated. Children need 10 to 14 days to acclimate.
You can also start acclimating while in cooler environments by wearing more clothing when exercising. This will raise the body temperature, which helps the body start sweating.
Acclimation helps you sweat for a longer time at a lower body temperature. Although this increases the amount you sweat, it decreases the amount of salt you lose in sweat or urine.
When to call for help during self-care
Call a doctor if any of the following occur during self-care at home:
Author: Ignite Healthwise, LLC Staff Clinical Review Board All Healthwise education is reviewed by a team that includes physicians, nurses, advanced practitioners, registered dieticians, and other healthcare professionals.
Clinical Review Board All Healthwise education is reviewed by a team that includes physicians, nurses, advanced practitioners, registered dieticians, and other healthcare professionals.
This information does not replace the advice of a doctor. Ignite Healthwise, LLC, disclaims any warranty or liability for your use of this information. Your use of this information means that you agree to the Terms of Use. Learn how we develop our content.
