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
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.
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
, such as colds and
bacterial infections, such as a
urinary tract infection or
pneumonia, often cause a fever.
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
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.
Health Tools help you make wise health decisions or take action to improve your health.
Symptoms of serious illness may
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”):
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
Certain health conditions and medicines weaken the immune system's ability to fight off infection and
illness. Some examples in adults 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:
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
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.
Severe trouble breathing means:
Moderate trouble breathing means:
Mild trouble breathing means:
Symptoms of difficulty breathing can range from mild to severe. For example:
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
You have answered all the questions. Based on your answers, you may be
able to take care of this problem at home.
Many things can affect how your body responds to a symptom and what kind
of care you may need. These include:
Severe dehydration means:
Moderate dehydration means:
Mild dehydration means:
Severe trouble breathing means:
Based on your answers, the problem may not improve without medical
Many prescription and non-prescription medicines can trigger
an allergic reaction and cause a fever. A few examples are:
Based on your answers, you need
or other emergency services now.
Based on your answers, you may need care soon. The
problem probably will not get better without medical care.
Based on your answers, you may need care right away. The problem is likely to get worse without medical care.
Shock is a life-threatening condition that may occur quickly
after a sudden illness or injury.
Symptoms of shock in a child may include:
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:
Fever can be a symptom of almost any type of infection.
Symptoms of a more serious infection may include the
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.
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
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
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
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
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
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 ofMay 27, 2016
Current as of:
May 27, 2016
William H. Blahd, Jr., MD, FACEP - Emergency Medicine
& Adam Husney, MD - Family Medicine & Kathleen Romito, MD - Family Medicine & David Messenger, MD
To learn more about Healthwise, visit Healthwise.org.
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