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 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.
Fever temperatures
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.
Causes of fever
Viral infections
, such as colds and influenza (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.
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
If a low body temperature is your only symptom, it is not something to worry about. If a low body temperature occurs with other symptoms, such as chills, shaking, breathing problems, or confusion, then this may be a sign of more serious illness.
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.
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 fluids.
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 L (2 qt) 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 L (1 quart ) purified water
- 2.5 mL (½ teaspoon) salt
- 30 mL (6 teaspoons) 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 [27°C (80°F) to32°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 at21°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.
Medicine you can buy without a prescription
Try a non-prescription medicine to help treat your fever or pain:
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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.
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Safety tips
Be sure to follow these safety tips when you use a non-prescription medicine:
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- 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 it.
- If you are or could be pregnant, do not take any medicine other than acetaminophen unless your doctor has told you to.
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Do not give aspirin to anyone younger than 18
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.
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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 treatment:
-
Level of consciousness
changes.
- 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.