A fever is a body temperature above 100.4°F. A normal oral temperature for a resting, healthy adult is about 98.6°F (37°C) (for someone over 70 normal temp is 96.8°F (36°C)). Your temperature can go up or down 1 to 2 degrees throughout the day. Fever is a sign of inflammation or infection and is a common symptom of illness. Fever is not a disease. A fever is one way your body fights illness—your body temperature goes up to kill bacteria that cannot live at the higher temperatures. Although it may not be comfortable, a temperature of up to 102°F is generally good for you. Most healthy adults can tolerate a fever as high as 103°F to 104°F for short periods of time without having problems. Body temperatures usually return to normal with the illness goes away.
Ranges in Body Temperatures
A temperature above 100.4°F (38°C) indicates a fever, called pyrexia in medical terms.
- Temperatures between 99°F (37.2°C) and 100.4°F (38°C) are called low-grade fever.
- Temperatures between 100.4°F (38°C) and 105.8°F (41°C) are called pyrexia.
- Temperatures between 105.8°F (41°C) and 109.4°F (43°C) are called hyperpyrexia and are serious.
- Temperatures above 109.4°F (43°C) are usually fatal, that is causing death.
Stages of Fever
A fever can be divided into three stages.
- Onset is when the temperature first begins to go up. The increase in temperature can be slow or sudden, the person can have chills and feel cold and breathing and heart rate increase.
- During the course of the fever the temperature can go up and down in one of three patterns: continuous, intermittent or remittent. During this stage, the person has an increased heart and breathing rate and feels warm to the touch. The person may also look flushed, feel thirsty, lose their appetite, have a headache and feel weak and tired.
- During the subsiding stage the temperature returns to normal. It can return gradually or suddenly. As the body temperature returns to normal, the person usually sweats and may become dehydrated due to loss of fluid from sweating.
How to Take Your Temperature
- Wash your hands with soap and warm water.
- Wash the thermometer in cold water.
- Make sure the top of the mercury is down near the bulb.
- To reset the thermometer, hold the thermometer firmly at the end opposite the mercury bulb and shake it with a downward flick of your wrist. This brings the mercury level down below the normal temperature level.
- Put the bulb end of the thermometer under your tongue and close your mouth. Keep your mouth closed while you take your temp.
- Wait 1 minute then take the thermometer out of your mouth. Hold the thermometer near light to read it; turn it slowly until you see the silver column of mercury. The number at the top of the mercury is your temperature. There is usually a mark on the thermometer showing a normal temperature at 98.6°F (37°C).
- Rinse the thermometer in cold water and clean it with alcohol before putting it away. Be sure to put it out of the reach of children because the mercury can be harmful if the thermometer is broken. What to Do if a Mercury Thermometer Breaks
Digital thermometers can also be used but they can be expensive to buy. They are easy to read, as they have a large digital display for numbers. Before using, make sure the thermometer is clean and turned on. Remove the thermometer once it beeps. Clean it before you put it away.
How to Treat a Fever
- Increase the amount of liquids you’re drinking, especially water. Your body may try to cool itself by sweating and you should replace this loss of fluid.
- Take your temperature every two hours. Each time you take your temperature, write down your temperature and the time you took it.
- Take your temperature before the end of two hours if your other symptoms change. For example, if you start throwing up or your temperature is going up each time you take it.
- For fevers that are uncomfortable, sponge the body with lukewarm, not cold. water. Take acetaminophen, aspirin, or ibuprofen to get your fever down. Do not give aspirin or products that contain aspirin to children or teens under the age of 20.
- Watch for signs of dehydration. Dehydration can happen if the fever causes you to sweat or you have other symptoms like vomiting or diarrhea. Signs of dehydration include: thirst, dry skin, dry mouth, chills, feeling tired or weak, and dark-colored urine.
When to Call Your Doctor
- If your fever is over 104°F and does not go down after two hours of home treatment.
- Persistent fever. Many viral illnesses, especially the flu, cause fevers of 102°F or higher for short periods of time (up to 12 to 24 hours).
- If the fever stays high:
- 102°F or higher for 2 full days
- 101°F or higher for 3 full days
- 100°F or higher for 4 full days
A fever is a symptom of a health problem and would be present along with other symptoms that mean you should call your doctor.
- If you think you may have the flu
- Fever over 103°F with dry skin, even under the armpits could mean possible heat stroke.
- If fever occurs along with other signs of a bacterial infection.
- If fever occurs along with the following symptoms:
- Very stiff neck and headache— you may have encephalitis or meningitis.
- Shortness of breath and cough—you may have bronchitis or pneumonia.
- Pain over eyes or cheekbone may indicate sinusitis or sinus infection.
- Painful or burning urination could mean a urinary tract infection
- Abdominal pain, nausea, and vomiting could mean flu, gastroenteritis, appendicitis or food poisoning
Fever in Newborns
Fever in newborns can be serious and should not be ignored.