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Topic Overview

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.

Normal body temperature

Most people have an average
body temperature of about
98.6°F (37°C), measured orally
(a thermometer is placed under the tongue). Your temperature may be as low as
97.4°F (36.3°C) in the morning
or as high as 99.6°F (37.6°C)
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.

Fever temperatures

A fever is a high body
temperature. A temperature of up to
102°F (38.9°C) can be helpful
because it helps the body fight infection. Most healthy children and adults can
tolerate a fever as high as
103°F (39.4°C) to
104°F (40°C) 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.

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.

Causes of fever

Viral infections, such as colds and
flu, 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
102°F (38.9°C) 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

Treating a fever

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.

Low body temperature

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.

Check Your Symptoms

Do you think you may have a fever or chills?
Fever or chills
Fever or chills
How old are you?
11 years or younger
11 years or younger
12 to 55 years
12 to 55 years
56 years or older
56 years or older
Are you male or female?
Are you pregnant?
Yes, you know that you’re pregnant.
No, you’re not pregnant, or you’re not sure if you’re pregnant.
Have you had surgery in the past 2 weeks?
Surgery within past 2 weeks
Surgery within past 2 weeks
Do you have symptoms of shock?
Symptoms of shock
Symptoms of shock
Do you think you may be dehydrated?
May be dehydrated
May be dehydrated
Are the symptoms severe, moderate, or mild?
Severe dehydration
Moderate dehydration
Mild dehydration
Are you having trouble drinking enough to replace the fluids you’ve lost?
Little sips of fluid usually are not enough. You need to be able to take in and keep down plenty of fluids.
Unable to maintain fluid intake
Able to maintain fluid intake
Are you having trouble breathing (more than a stuffy nose)?
Difficulty breathing more than a stuffy nose
Difficulty breathing more than a stuffy nose
Would you describe the breathing problem as severe, moderate, or mild?
Severe difficulty breathing
Moderate difficulty breathing
Mild difficulty breathing
Is your ability to breathe:
Getting worse?
Breathing problems are getting worse
Staying about the same (not better or worse)?
Breathing problems are unchanged
Getting better?
Breathing problems are getting better
Suddenly drooling and unable to swallow
Suddenly drooling and unable to swallow
Symptoms of serious illness
Symptoms of serious illness
Is there any pain?
How bad is the pain on a scale of 0 to 10, if 0 is no pain and 10 is the worst pain you can imagine?
8 to 10: Severe pain
Severe pain
5 to 7: Moderate pain
Moderate pain
1 to 4: Mild pain
Mild pain
Do you have a health problem or take medicine that weakens your immune system?
Disease or medicine that causes immune system problems
Disease or medicine that causes immune system problems
Do you have shaking chills or very heavy sweating?
Shaking chills are a severe, intense form of shivering. Heavy sweating means that sweat is pouring off you or soaking through your clothes.
Shaking chills or heavy sweating
Shaking chills or heavy sweating
Besides fever, do you have other symptoms of a more serious infection?
Symptoms of more serious infection
Symptoms of more serious infection
Have tiny red or purple spots or bruises appeared suddenly?
Sudden appearance of red or purple spots or bruising
Sudden appearance of red or purple spots or bruising
Do you have a rash that looks like a sunburn?
Sunburn-like rash
Sunburn-like rash
Did you take your temperature?
Temperature taken
Temperature taken
How high is the fever? The answer may depend on how you took the temperature.
High: 104°F (40°C) or higher, oral
High fever: 104°F (40°C) or higher, oral
Moderate: 100.4°F (38°C) to 103.9°F (39.9°C), oral
Moderate fever: 100.4°F (38°C) to 103.9°F (39.9°C), oral
Mild: 100.3°F (37.9°C) or lower, oral
Mild fever: 100.3°F (37.9°C) or lower, oral
How high do you think the fever is?
Feels fever is high
Feels fever is moderate
Mild or low
Feels fever is mild
How long have you had a fever?
Less than 2 days (48 hours)
Fever for less than 2 days
At least 2 days but less than 1 week
Fever for at least 2 days but less than 1 week
1 week or more
Fever for 1 week or more
Do you think that a medicine or a vaccine may be causing the fever?
Think about whether the fever started soon after you began using a new medicine or a higher dose of a medicine. Or did it start after you got a shot or vaccine?
Medicine may be causing the fever
Medicine may be causing the fever

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
  • Medicines you take. Certain
    medicines, herbal remedies, and supplements can cause symptoms or make them
  • 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
  • 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.

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 may feel tired and edgy (mild dehydration), or
    you may feel weak, not alert, and not able to think clearly (severe
  • You may pass less urine than usual (mild
    dehydration), or you may not be passing urine at all (severe

Severe dehydration means:

  • Your mouth and eyes may be extremely
  • You may pass little or no urine for 12 or more
  • You may not feel alert or be able to think
  • You may be too weak or dizzy to stand.
  • You may
    pass out.

Moderate dehydration means:

  • You may be a lot more thirsty than
  • Your mouth and eyes may be drier than usual.
  • You may
    pass little or no urine for 8 or more hours.
  • You may feel dizzy
    when you stand or sit up.

Mild dehydration means:

  • You may be more thirsty than usual.
  • You may pass less urine than usual.

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
  • You do not feel alert or cannot think clearly.

Moderate trouble breathing means:

  • It’s hard to talk in full
  • 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
  • The child has to take breaks from eating or talking to
  • 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.

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.

Many prescription and nonprescription medicines can trigger
an allergic reaction and cause a fever. A few examples are:

  • Antibiotics.
  • Barbiturates, such as
  • Aspirin, if you take too much.

If you’re not sure if a fever is high, moderate, or mild,
think about these issues:

With a high fever:

  • You feel very hot.
  • It is likely one of
    the highest fevers you’ve ever had. High fevers are not that common, especially
    in adults.

With a moderate fever:

  • You feel warm or hot.
  • You know you have
    a fever.

With a mild fever:

  • You may feel a little warm.
  • You think
    you might have a fever, but you’re not sure.

Certain health conditions and medicines weaken the immune system’s ability to fight off infection and
illness. Some examples in adults are:

  • Diseases such as diabetes, cancer, heart disease,
    and HIV/AIDS.
  • Long-term alcohol and drug
  • Steroid medicines, which may be used to treat a variety
    of conditions.
  • Chemotherapy and radiation therapy for
  • Other medicines used to treat autoimmune
  • Medicines taken after organ transplant.
  • Not
    having a spleen.

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

  • High:
    104°F (40°C) and
  • Moderate:
    100.4°F (38°C) to
    103.9°F (39.9°C)
  • Mild:
    100.3°F (37.9°C) and

A forehead (temporal) scanner is usually 0.5°F (0.3°C) to 1°F (0.6°C) lower than an oral temperature.

Ear or rectal temperature

  • High:
    105°F (40.6°C) and
  • Moderate:
    101.4°F (38.6°C) to
    104.9°F (40.5°C)
  • Mild:
    101.3°F (38.5°C) and

Armpit (axillary) temperature

  • High: 103°F (39.5°C) and higher
  • Moderate:
    99.4°F (37.4°C) to
    102.9°F (39.4°C)
  • Mild: 99.3°F (37.3°C) and lower

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”):

  • Are tiny, flat red or purple spots in the skin or
    the lining of the mouth.
  • Do not turn white when you press on
  • Range from the size of a pinpoint to the size of a small pea and do not itch or cause pain.
  • May spread over a large area of the body within a few hours.
  • Are different than tiny, flat red spots or birthmarks that are
    present all the time.

Purpura (say “PURR-pyuh-ruh” or “PURR-puh-ruhâ€):

  • Is sudden, severe bruising that occurs for no clear
  • May be in one area or all over.
  • Is different
    than the bruising that happens after you bump into something.

Symptoms of serious illness may

  • A severe headache.
  • A stiff
  • Mental changes, such as feeling confused or much less
  • Extreme fatigue (to the point where it’s hard for you to
  • Shaking chills.

Pain in adults and older children

  • Severe pain (8 to 10): The pain
    is so bad that you can’t stand it for more than a few hours, can’t sleep, and
    can’t do anything else except focus on the pain.
  • Moderate pain (5 to 7): The pain is bad enough to disrupt your
    normal activities and your sleep, but you can tolerate it for hours or days.
    Moderate can also mean pain that comes and goes even if it’s severe when it’s
  • Mild pain (1 to 4): You notice the pain,
    but it is not bad enough to disrupt your sleep or activities.

Pain in children under 3 years

It can be hard to tell how much pain a baby or toddler is in.

  • Severe pain (8 to 10): The
    pain is so bad that the baby cannot sleep, cannot get comfortable, and cries
    constantly no matter what you do. The baby may kick, make fists, or
  • Moderate pain (5 to 7): The baby is
    very fussy, clings to you a lot, and may have trouble sleeping but responds
    when you try to comfort him or her.
  • Mild pain (1 to 4): The baby is a little fussy and clings to you a little but responds
    when you try to comfort him or her.

Fever can be a symptom of almost any type of infection.
Symptoms of a more serious infection may include the

  • Skin infection: Pain,
    redness, or pus
  • Joint infection: Severe
    pain, redness, or warmth in or around a joint
  • Bladder infection: Burning when you urinate, and a frequent
    need to urinate without being able to pass much urine
  • Kidney infection: Pain in the flank, which is either side of
    the back just below the rib cage
  • Abdominal infection: Belly pain

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:

  • Passing out (losing consciousness).
  • Feeling very dizzy or
    lightheaded, like you may pass out.
  • Feeling very weak or having
    trouble standing.
  • Not feeling alert or able to think clearly. You
    may be confused, restless, fearful, or unable to respond to questions.

Shock is a life-threatening condition that may occur quickly
after a sudden illness or injury.

Symptoms of shock in a child may include:

  • Passing out (losing consciousness).
  • Being very sleepy or hard
    to wake up.
  • Not responding when being touched or talked to.
  • Breathing much faster than usual.
  • Acting confused.
    The child may not know where he or she is.

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.

Seek Care Today

Based on your answers, you may need care soon. The
problem probably will not get better without medical care.

  • 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

Call 911 Now

Based on your answers, you need
emergency care.

Call 911 or other emergency services now.

Make an Appointment

Based on your answers, the problem may not improve without medical

  • Make an appointment to see your doctor in the
    next 1 to 2 weeks.
  • If appropriate, try home treatment while you
    are waiting for the appointment.
  • If symptoms get worse or you have
    any concerns, call your doctor. You may need care sooner.
Fever or Chills, Age 11 and Younger
Pregnancy-Related Problems
Postoperative Problems

Home Treatment

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

Adults and children age 12 and older

If you become
mildly to moderately dehydrated:

  • Stop your activity and rest.
  • Drink a rehydration drink, water, juice, or sports
    drink to replace fluids and minerals. Drink 2 qt (2 L) of cool liquids over
    the next 2 to 4 hours. You should drink at least 10 glasses of liquid a day to
    replace lost fluids. You can make an inexpensive rehydration drink at home. But
    do not give this homemade drink to children younger than 12. Measure all ingredients precisely. Small variations can make the
    drink less effective or even harmful. Mix the following:

    • 1 quart (1 L) purified water
    • ½ teaspoon (2.5 mL) salt
    • 6 teaspoons (30 mL) sugar

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 [80°F (27°C) to
90°F (32°C)]
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 pajamas or a light undershirt. Do not wear very
warm clothing or use heavy bed covers. Keep room temperature at
70°F (21°C)
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.

Medicine you can buy without a prescription
Try a nonprescription
medicine to help treat your fever or pain:

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.

Safety tips
Be sure to follow these
safety tips when you use a nonprescription medicine:
  • Carefully read and follow all directions
    on the medicine bottle and box.
  • Do not take more than the
    recommended dose.
  • Do not take a medicine if you have had an
    allergic reaction to it in the past.
  • If
    you have been told to avoid a medicine, call your doctor before you take
  • If you are or could be pregnant, do not take any medicine other
    than acetaminophen unless your doctor has told you to.
  • Do not give aspirin to anyone younger than age 20 unless your doctor tells you to.
  • Do
    not give your child naproxen (such as Aleve) to children younger than
    age 12 unless your child’s doctor tells you to.

Be sure to check your temperature every 2 to 4 hours to make
sure home treatment is working.

Symptoms to watch for during home treatment

Call your doctor if any of the following occur during home

  • Level of consciousness
  • You have
    signs of dehydration and you are unable to drink
    enough to replace lost fluids. Signs of dehydration include being thirstier than usual and having darker urine than usual.
  • Other symptoms develop, such as pain in one area of the body,
    shortness of breath, or urinary symptoms.
  • Symptoms become more severe or frequent.


The best way to prevent fevers is to reduce
your exposure to infectious diseases.
Hand-washing 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.

Preparing For Your Appointment

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:

  • What is the history of your fever?
    • When did you fever start?
    • How
      often do you have a fever?
    • How long does your fever
    • Does your fever have a pattern?
    • Are you able to
      measure your temperature? How high is your fever?
  • Have you had any other health problems over the
    past 3 months?
  • Have you recently been exposed to anyone who has a
  • Have you recently traveled outside the country or been
    exposed to immigrants or other nonnative people?
  • Have you had any
    insect bites in the past 6 weeks, including tick bites?
  • Have you had an immunization (vaccine) shot recently?
  • What home
    treatment measures you have tried? Did they help?
  • What
    nonprescription medicines have you taken? Did they help? Keep a fever chart of
    what your temperature was before and after home treatment.
  • Do you
    have any
    health risks?

Other Places To Get Help


Centers for Disease Control and Prevention: Travelers’ Health (U.S.)


ByHealthwise Staff
Primary Medical Reviewer William H. Blahd, Jr., MD, FACEP – Emergency Medicine
Kathleen Romito, MD – Family Medicine
Adam Husney, MD – Family Medicine
Specialist Medical Reviewer H. Michael O’Connor, MD – Emergency Medicine
David Messenger, MD

Current as ofMay 25, 2017