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.
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 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
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 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 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.
Check your symptoms to decide if and when you should see a doctor.
Check Your Symptoms
The medical assessment of symptoms is based on the body parts you have.
- If you are transgender or nonbinary, choose the sex that matches the body parts (such as ovaries, testes, prostate, breasts, penis, or vagina) you now have in the area where you are having symptoms.
- If your symptoms aren’t related to those organs, you can choose the gender you identify with.
- If you have some organs of both sexes, you may need to go through this triage tool twice (once as "male" and once as "female"). This will make sure that the tool asks the right questions for you.
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 sooner.
- Medicines you take. Certain medicines, herbal remedies, and supplements can cause symptoms or make them worse.
- 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 symptoms.
- 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 example:
- You may feel tired and edgy (mild dehydration), or you may feel weak, not alert, and not able to think clearly (severe dehydration).
- You may pass less urine than usual (mild dehydration), or you may not be passing urine at all (severe dehydration).
Severe dehydration means:
- Your mouth and eyes may be extremely dry.
- You may pass little or no urine for 12 or more hours.
- You may not feel alert or be able to think clearly.
- You may be too weak or dizzy to stand.
- You may pass out.
Moderate dehydration means:
- You may be a lot more thirsty than usual.
- 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 air.
- You do not feel alert or cannot think clearly.
Moderate trouble breathing means:
- It's hard to talk in full sentences.
- 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 usual.
- The child has to take breaks from eating or talking to breathe.
- 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 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 nonprescription medicines can trigger an allergic reaction and cause a fever. A few examples are:
- Barbiturates, such as phenobarbital.
- 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 problems.
- Steroid medicines, which may be used to treat a variety of conditions.
- Chemotherapy and radiation therapy for cancer.
- Other medicines used to treat autoimmune disease.
- 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 higher
- Moderate: 100.4°F (38°C) to 103.9°F (39.9°C)
- Mild: 100.3°F (37.9°C) and lower
A forehead (temporal) scanner is usually 0.5°F (0.3°C) to 1°F (0.6°C) lower than an oral temperature.
- High: 105°F (40.6°C) and higher
- Moderate: 101.4°F (38.6°C) to 104.9°F (40.5°C)
- Mild: 101.3°F (38.5°C) and lower
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 them.
- 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-ruh”):
- Is sudden, severe bruising that occurs for no clear reason.
- 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 include:
- A severe headache.
- A stiff neck.
- Mental changes, such as feeling confused or much less alert.
- Extreme fatigue (to the point where it's hard for you to function).
- 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 there.
- 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 grimace.
- 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 following:
- 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.
Adults and older children often have several symptoms of shock. These 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.
Babies and young children often have several symptoms of shock. These 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 sooner.
Call 911 Now
Based on your answers, you need emergency care.
Call 911 or other emergency services now.
Sometimes people don't want to call 911. They may think that their symptoms aren't serious or that they can just get someone else to drive them. Or they might be concerned about the cost. But based on your answers, the safest and quickest way for you to get the care you need is to call 911 for medical transport to the hospital.
Make an Appointment
Based on your answers, the problem may not improve without medical care.
- 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.
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 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.
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.
Be sure to follow these safety tips when you use a nonprescription medicine:
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.
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 topicMaking 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 last?
- 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 fever?
- 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?
- Respiratory Problems, Age 11 and Younger
- Sore Throat and Other Throat Problems
- Ear Problems and Injuries, Age 11 and Younger
- Urinary Problems and Injuries, Age 12 and Older
- Abdominal Pain, Age 11 and Younger
- Abdominal Pain, Age 12 and Older
- Respiratory Problems, Age 12 and Older
- Ear Problems and Injuries, Age 12 and Older
- Urinary Problems and Injuries, Age 11 and Younger
- Fever Seizures
Current as of: June 26, 2019
Author: Healthwise Staff
William H. Blahd Jr. MD, FACEP - Emergency Medicine
Kathleen Romito MD - Family Medicine
Adam Husney MD - Family Medicine
H. Michael O'Connor MD - Emergency Medicine
David Messenger MD - Emergency Medicine, Critical Care Medicine
Current as of: June 26, 2019