Fever is the body's normal and healthy reaction to infection and other illnesses, both minor and serious. It helps the body fight infection. Fever is a symptom, not a disease. In most cases, having a fever means you have a minor illness. When you have a fever, your other symptoms will help you determine how serious your illness is.
Temperatures in this topic are oral temperatures. Oral temperatures are usually taken in older children and adults. To convert a temperature from one method (such as the ear) to another, use the Interactive Tool: How Do Temperatures Compare?
Most people have an average body temperature of about 37°C (98.6°F), measured orally (a thermometer is placed under the tongue). Your temperature may be as low as 36.3°C (97.4°F) in the morning or as high as 37.6°C (99.6°F) in the late afternoon. Your temperature may go up when you exercise, wear too many clothes, take a hot bath, or are exposed to hot weather.
A fever is a high body temperature. A temperature of up to 38.9°C (102°F) can be helpful because it helps the body fight infection. Most healthy children and adults can tolerate a fever as high as 39.4°C (103°F) to 40°C (104°F) for short periods of time without problems. Children tend to have higher fevers than adults.
The degree of fever may not show how serious the illness is. With a minor illness, such as a cold, you may have a temperature, while a very serious infection may cause little or no fever. It is important to look for and evaluate other symptoms along with the fever.
If you are not able to measure your temperature with a thermometer, you need to look for other symptoms of illness. A fever without other symptoms that lasts 3 to 4 days, comes and goes, and gradually reduces over time is usually not a cause for concern. When you have a fever, you may feel tired, lack energy, and not eat as much as usual. High fevers are not comfortable, but they rarely cause serious problems.
Oral temperature taken after smoking or drinking a hot fluid may give you a false high temperature reading. After drinking or eating cold foods or fluids, an oral temperature may be falsely low. For information on how to take an accurate temperature, see the topic Body Temperature.
, such as colds and flu, and bacterial infections, such as a urinary tract infection or pneumonia, often cause a fever.
Travel outside your native country can expose you to other diseases. Fevers that begin after travel in other countries need to be evaluated by your doctor.
Fever and respiratory symptoms are hard to evaluate during the flu season. A fever of 38.9°C (102°F) or higher for 3 to 4 days is common with the flu. For more information, see the topic Respiratory Problems, Age 12 and Older.
Recurrent fevers are those that occur 3 or more times within 6 months and are at least 7 days apart. Each new viral infection may cause a fever. It may seem that a fever is ongoing, but if 48 hours pass between fevers, then the fever is recurring. If you have frequent or recurrent fevers, it may be a symptom of a more serious problem. Talk to your doctor about your fevers.
In most cases, the illness that caused the fever will clear up in a few days. You usually can treat the fever at home if you are in good health and do not have any medical problems or significant symptoms with the fever. Make sure that you are taking enough foods and fluids and urinating in normal amounts.
An abnormally low body temperature (hypothermia) can be serious, even life-threatening. Low body temperature may occur from cold exposure, shock, alcohol or drug use, or certain metabolic disorders, such as diabetes or hypothyroidism. A low body temperature may also be present with an infection, particularly in newborns, older adults, or people who are frail. An overwhelming infection, such as sepsis, may also cause an abnormally low body temperature.
Check your symptoms to decide if and when you should see a doctor.
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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.
You can get dehydrated when you lose a lot of fluids because of problems like vomiting or fever.
Symptoms of dehydration can range from mild to severe. For example:
Severe dehydration means:
Moderate dehydration means:
Mild dehydration means:
Symptoms of difficulty breathing can range from mild to severe. For example:
Severe trouble breathing means:
Moderate trouble breathing means:
Mild trouble breathing means:
Severe trouble breathing means:
Sudden drooling and trouble swallowing can be signs of a serious problem called epiglottitis. This problem can happen at any age.
The epiglottis is a flap of tissue at the back of the throat that you can't see when you look in the mouth. When you swallow, it closes to keep food and fluids out of the tube (trachea) that leads to the lungs. If the epiglottis becomes inflamed or infected, it can swell and quickly block the airway. This makes it very hard to breathe.
The symptoms start suddenly. A person with epiglottitis is likely to seem very sick, have a fever, drool, and have trouble breathing, swallowing, and making sounds. In the case of a child, you may notice the child trying to sit up and lean forward with his or her jaw forward, because it's easier to breathe in this position.
Many prescription and non-prescription medicines can trigger an allergic reaction and cause a fever. A few examples are:
If you're not sure if a fever is high, moderate, or mild, think about these issues:
With a high fever:
With a moderate fever:
With a mild fever:
Certain health conditions and medicines weaken the immune system's ability to fight off infection and illness. Some examples in adults are:
Temperature varies a little depending on how you measure it. For adults and children age 12 and older, these are the ranges for high, moderate, and mild, according to how you took the temperature.
Oral (by mouth) temperature
A forehead (temporal) scanner is usually 0.3 C (0.5 F) to 0.6 C (1 F) lower than an oral temperature
Ear or rectal temperature
Armpit (axillary) temperature
Sudden tiny red or purple spots or sudden bruising may be early symptoms of a serious illness or bleeding problem. There are two types.
Petechiae (say "puh-TEE-kee-eye"):
Purpura (say "PURR-pyuh-ruh" or “PURR-puh-ruh”):
Symptoms of serious illness may include:
Pain in adults and older children
Pain in children under 3 years
It can be hard to tell how much pain a baby or toddler is in.
Fever can be a symptom of almost any type of infection. Symptoms of a more serious infection may include the following:
Shock is a life-threatening condition that may quickly occur after a sudden illness or injury.
Symptoms of shock (most of which will be present) include:
Shock is a life-threatening condition that may occur quickly after a sudden illness or injury.
Symptoms of shock in a child may include:
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 may need care soon. The problem probably will not get better without medical care.
Based on your answers, you need emergency care.
or other emergency services now.
Based on your answers, the problem may not improve without medical care.
It's easy to become dehydrated when you have a fever.
In the early stages, you may be able to correct mild to moderate dehydration with home treatment measures. It is important to control fluid losses and replace lost fluids.
If you become mildly to moderately dehydrated:
Rest and take it easy for 24 hours, and continue to drink a lot of fluids. Although you will probably start feeling better within just a few hours, it may take as long as a day and a half to completely replace the fluid that you lost.
Many people find that taking a lukewarm [27°C (80°F) to 32°C (90°F)] shower or bath makes them feel better when they have a fever. Do not try to take a shower if you are dizzy or unsteady on your feet. Increase the water temperature if you start to shiver. Shivering is a sign that your body is trying to raise its temperature. Do not use rubbing alcohol, ice, or cold water to cool your body.
Dress lightly when you have a fever. This will help your body cool down. Wear light pyjamas or a light undershirt. Do not wear very warm clothing or use heavy bed covers. Keep room temperature at 21°C (70°F) or lower.
If you are not able to measure your temperature, you need to look for other symptoms of illness every hour while you have a fever and follow home treatment measures.
Talk to your child's doctor before switching back and forth between doses of acetaminophen and ibuprofen. When you switch between two medicines, there is a chance your child will get too much medicine.
Be sure to check your temperature every 2 to 4 hours to make sure home treatment is working.
Call your doctor if any of the following occur during home treatment:
The best way to prevent fevers is to reduce your exposure to infectious diseases. Handwashing is the single most important prevention measure for people of all ages.
Immunizations can reduce the risk for fever-related illnesses, such as the flu. Although no vaccine is 100% effective, most routine immunizations are effective for 85% to 95% of the people who receive them. For more information, see the topic Immunizations.
To prepare for your appointment, see the topic Making the Most of Your Appointment.
You can help your doctor diagnose and treat your condition by being prepared to answer the following questions:
ByHealthwise StaffPrimary Medical ReviewerWilliam H. Blahd, Jr., MD, FACEP - Emergency MedicineAdam Husney, MD - Family MedicineKathleen Romito, MD - Family MedicineSpecialist Medical ReviewerDavid Messenger, MD
Current as ofJune 14, 2017
Current as of: June 14, 2017
William H. Blahd, Jr., MD, FACEP - Emergency Medicine
& Adam Husney, MD - Family Medicine & Kathleen Romito, MD - Family Medicine & David Messenger, MD
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