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Home > Health Library > Heat-Related Illnesses
A healthy body temperature is maintained by the nervous system. As the body temperature increases, the body tries to maintain 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 rapidly 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 environments may quickly develop 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 cannot transfer heat effectively or because external heat gain is excessive.
Heat-related illnesses include:
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. Exercising during hot weather, working outdoors, and overdressing for the environment increase your risk. 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 alter your sense of thirst or increase your body's production of 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:
Most heat-related illnesses can be prevented by keeping the body cool and by avoiding dehydration in hot environments. Home treatment is usually all that is needed to treat mild heat-related illnesses. Heat exhaustion and heatstroke need immediate medical treatment.
Check your symptoms to decide if and when you should see a doctor.
Many things can affect how your body responds to a symptom and what kind of care you may need. These include:
You have answered all the questions. Based on your answers, you may be able to take care of this problem at home.
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:
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:
Severe trouble breathing means:
Moderate trouble breathing means:
Mild trouble breathing means:
If you have symptoms of heat exhaustion, try the following first aid to cool off:
Signs that heat exhaustion is becoming severe include:
Some other symptoms of heat-related illness include:
Symptoms of heatstroke may include:
Heatstroke occurs when the body can't control its own temperature and body temperature continues to rise.
Based on your answers, you may need care right away. The problem is likely to get worse without medical care.
Based on your answers, you need emergency care.
Call911or other emergency services now.
Based on your answers, you may need care soon.
Call your doctor today to discuss the symptoms and arrange for care.
Try First Aid for Symptoms
If your symptoms get better, you may not need to seek care today.
Based on your answers, you may need care soon. The problem probably will not get better without medical care.
While you wait for help to arrive:
Emergency first aid for heatstroke is needed immediately because this condition is life-threatening. After calling 911 or other emergency medical services, follow these first aid steps:
When recognized in the early stages, most heat-related illnesses, such as mild heat exhaustion, can be treated at home.
If your child is dehydrated, see the topic Dehydration for information about home treatment.
Heat syncope (fainting) usually does not last long and improves when you lie down to a flat position. It is helpful to lie in a cooler environment.
Heat edema (swelling) is treated with rest and by elevating your legs. If you are standing for a long time in a hot environment, flex your leg muscles often so that blood does not pool 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 are not on a salt- (sodium-) restricted diet, eat a little more salt, such as a few nuts or pretzels. Do not use salt tablets, because they are absorbed slowly and can cause irritation of the stomach. Try massaging and stretching your cramped muscles.
Heat rash (prickly heat) usually gets better and goes away without treatment. Antihistamines may help if you are having problems with itching. Keep areas clean and dry to help prevent a skin infection. Do not use baby powder while a rash is present. The powder can build up in the skin creases and hold moisture, allowing the growth of bacteria that may cause infection. Dress in as few clothes as possible during hot weather. Keep your home, especially sleeping areas, cool.
Call your doctor if any of the following occur during home treatment:
The following tips may help prevent a heat-related illness. Be aware of the symptoms of heat-related illnesses and the warning signs of dehydration.
Staying physically fit can help you acclimate to a hot environment. Before you travel to or work in a hotter environment, use gradual physical conditioning. This takes about 8 to 14 days for adults. Children require 10 to 14 days for their bodies to acclimate to the heat. If you travel to a hot environment and are not accustomed to the heat, cut your usual outside physical activities in half for the first 4 to 5 days. Gradually increase your activities after your body adjusts to the heat and level of activity.
Be aware that when the outdoor humidity is greater than 75%, the body's ability to lose heat by sweating is decreased. Other ways of keeping cool need to be used. The National Weather Service lists a heat index each day in the newspaper to alert people of the risk for a heat-related illness in relation to the air temperature and humidity of that day. Direct exposure to the sun can increase the risk of a heat-related illness on days when the heat index is high.
People who have had heatstroke in the past may be more sensitive to the effects of heat in the first few months following the illness, but they do not have long-term problems.
To prepare for your appointment, see the topicMaking the Most of Your Appointment.
You can help your doctor diagnose and treat your condition by being prepared to answer the following questions:
Other Works Consulted
Lipman GS, et al. (2013). Wilderness Medical Society practice guidelines for the prevention and treatment of heat-related illness. Wilderness and Environmental Medicine, 24(4): 351–361.
Current as of:
June 26, 2019
Author: Healthwise StaffMedical Review: William H. Blahd Jr. MD, FACEP - Emergency MedicineAdam Husney MD - Family MedicineKathleen Romito MD - Family Medicine
Current as of:
June 26, 2019
Medical Review:William H. Blahd Jr. MD, FACEP - Emergency Medicine & Adam Husney MD - Family Medicine & Kathleen Romito MD - Family Medicine
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