Fever, also known as pyrexia and febrile response, is defined as having a temperature above the normal range due to an increase in the body’s temperature set-point. There is not a single agreed-upon upper limit for normal temperature with sources using values between 37.5 and 38.3 °C (99.5 and 100.9 °F). The increase in set-point triggers increased muscle contraction and causes a feeling of cold. This results in greater heat production and efforts to conserve heat. When the set-point temperature returns to normal, a person feels hot, becomes flushed, and may begin to sweat. Rarely a fever may trigger a febrile seizure. This is more common in young children. Fevers do not typically go higher than 41 to 42 °C (105.8 to 107.6 °F).
A fever can be caused by many medical conditions ranging from not serious to potentially serious. This includes viral, bacterial and parasitic infections such as the common cold, urinary tract infections, meningitis, malaria and appendicitis among others. Non-infectious causes include vasculitis, deep vein thrombosis, side effects of medication, and cancer among others. It differs from hyperthermia, in that hyperthermia is an increase in body temperature over the temperature set-point, due to either too much heat production or not enough heat loss.
Treatment to reduce fever is generally not required. Treatment of associated pain and inflammation, however, may be useful and help a person rest. Medications such as ibuprofen or paracetamol may help with this as well as lower temperature. Measures such as putting a cool damp cloth on the forehead and having a slightly warm bath are not useful and may simply make a person more uncomfortable. Children younger than three months require medical attention, as might people with serious medical problems such as a compromised immune system or people with other symptoms. Hyperthermia does require treatment.
Fever is one of the most common medical signs. It is part of about 30% of healthcare visits by children and occurs in up to 75% of adults who are seriously sick. While fever is a useful defense mechanism, treating fever does not appear to worsen outcomes. Fever is viewed with greater concern by parents and healthcare professionals than it usually deserves, a phenomenon known as fever phobia.
Fever occurs when an area in your brain called the hypothalamus (hi-poe-THAL-uh-muhs) — also known as your body’s “thermostat” — shifts the set point of your normal body temperature upward. When this happens, you may feel chilled and add layers of clothing or wrap up in a blanket, or you may shiver to generate more body heat, eventually resulting in an elevated body temperature.
Normal body temperature varies throughout the day — it’s lower in the morning and higher in the late afternoon and evening. Although most people consider 98.6 F (37 C) normal, your body temperature can vary by a degree or more — from about 97 F (36.1 C) to 99 F (37.2 C) — and still be considered normal. Factors such as your menstrual cycle or heavy exercise can affect your temperature.
Fever or elevated body temperature might be caused by:
- A virus
- A bacterial infection
- Heat exhaustion
- Extreme sunburn
- Certain inflammatory conditions such as rheumatoid arthritis — inflammation of the lining of your joints (synovium)
- A malignant tumor
- Some medications, such as antibiotics and drugs used to treat high blood pressure or seizures
- Some immunizations, such as the diphtheria, tetanus and acellular pertussis (DTaP) or pneumococcal vaccine
Sometimes the cause of a fever can’t be identified. If you have a temperature of 101 F (38.3 C) or higher for more than three weeks and your doctor isn’t able to find the cause after extensive evaluation, the diagnosis may be fever of unknown origin.
- Age: Children are at greater risk of contracting any disease and developing fever. Children in preschool and elementary school can experience six to 12 colds per year often associated with fever and adolescents and adults usually have two to four colds per year which may or may not be associated with fever.
- Contact: Being in close contact with a person who is sick increases your risk of catching the infection and fever.
- Immunity: People with weak immune system (weakened by medications such as corticosteroids or diseases such as HIV/AIDS) are at increased risk of developing any infection and fever.
- Food and water: Having contaminated food or water increases the risk of infection and fever.
You have a fever when your temperature rises above its normal range. What’s normal for you may be a little higher or lower than the average normal temperature of 98.6 F (37 C).
Depending on what’s causing your fever, additional fever signs and symptoms may include:
- Muscle aches
- Loss of appetite
- General weakness
High fevers between 103 F (39.4 C) and 106 F (41.1 C) may cause:
When to see a doctor
Fevers by themselves may not be a cause for alarm — or a reason to call a doctor. Yet there are some circumstances when you should seek medical advice for your baby, your child or yourself.
Taking a temperature
To check your or your child’s temperature, you can choose from several types of thermometers, including oral, rectal, ear (tympanic) and forehead (temporal artery) thermometers.
Although it’s not the most accurate way to take a temperature, you can use an oral thermometer for an armpit (axillary) reading:
- Place the thermometer in the armpit and cross your arms or your child’s arms over the chest.
- Wait four to five minutes. The axillary temperature is slightly lower than an oral temperature.
- If you call your doctor, report the actual number on the thermometer and where on the body you took the temperature.
Use a rectal thermometer for infants:
- Place a dab of petroleum jelly on the bulb.
- Lay your baby on his or her tummy.
- Carefully insert the bulb 1/2 to 1 inch into your baby’s rectum.
- Hold the bulb and your baby still for three minutes.
- Don’t let go of the thermometer while it’s inside your baby. If your baby squirms, the thermometer could go deeper and cause an injury.
An unexplained fever is greater cause for concern in infants and in children than in adults. Call your baby’s doctor if your child is:
- Younger than age 3 months and has a rectal temperature of 100.4 F (38 C) or higher.
- Between ages 3 to 6 months and has a temperature up to 102 F (38.9 C) and seems unusually irritable, lethargic or uncomfortable or has a temperature higher than 102 F (38.9 C).
- Between ages 6 to 24 months and has a temperature higher than 102 F (38.9 C) that lasts longer than one day but shows no other symptoms. If your child also has other signs and symptoms, such as a cold, cough or diarrhea, you might call your child’s doctor sooner based on severity.
- A newborn and has a lower than normal temperature — less than 97 F (36.1 C). Very young babies may not regulate body temperature well when they’re ill and may become cold rather than hot.
When in doubt, go ahead and call your child’s doctor, whether you think your baby’s temperature is abnormally high or abnormally low.
There’s probably no cause for alarm if your child has a fever but is responsive — making eye contact with you and responding to your facial expressions and to your voice — and is drinking fluids and playing.
Call your child’s doctor if your child:
- Is listless or irritable, vomits repeatedly, has a severe headache or stomachache, or has any other symptoms causing significant discomfort.
- Has a fever after being left in a hot car. Seek medical care immediately.
- Has a fever that lasts longer than three days (in children age 2 and older).
- Appears listless and has poor eye contact with you.
Ask your child’s doctor for guidance in special circumstances, such as a child with immune system problems or with a pre-existing illness. Your child’s doctor may also recommend precautions if your child has just started taking a new prescription medicine.
Call your doctor if:
- Your temperature is 103 F (39.4 C) or higher
- You’ve had a fever for more than three days
In addition, seek immediate medical attention if any of these signs or symptoms accompanies a fever:
- Severe headache
- Severe throat swelling
- Unusual skin rash, especially if the rash rapidly worsens
- Unusual sensitivity to bright light
- Stiff neck and pain when you bend your head forward
- Mental confusion
- Persistent vomiting
- Difficulty breathing or chest pain
- Extreme listlessness or irritability
- Abdominal pain or pain when urinating
- Muscle weakness or sensory changes, which might indicate a problem with your nerves, spinal cord or brain function (focal neurologic deficit)
- Any other unexplained signs or symptoms
To evaluate a fever, your doctor may:
- Ask questions about your symptoms and medical history
- Perform a physical exam
- Order tests, such as blood tests or a chest X-ray, as needed, based on your medical history and physical exam
Because a fever can indicate a serious illness in a young infant, especially one 28 days or younger, your baby might be admitted to the hospital for testing and treatment.
For a low-grade fever, your doctor may not recommend treatment to lower your body temperature. Doing so may prolong the illness or mask symptoms and make it harder to determine the cause.
In the case of a high fever, your doctor may recommend an over-the-counter medication, such as:
- Acetaminophen (Tylenol, others) or ibuprofen (Advil, Motrin IB, others). Use these medications according to the label instructions or as recommended by your doctor. Be careful to avoid taking too much. High doses or long-term use of acetaminophen may cause liver or kidney damage, and acute overdoses can be fatal. If your child’s fever remains high after a dose, don’t give more medication; call your doctor instead. For temperatures below 102 F (38.9 C), don’t use fever-lowering drugs unless advised by your doctor.
- Aspirin, for adults only. Don’t give aspirin to children, because it may trigger a rare, but potentially fatal, disorder known as Reye’s syndrome.
Depending on the cause of your fever, your doctor may prescribe an antibiotic, especially if he or she suspects a bacterial infection, such as pneumonia or strep throat.
Antibiotics don’t treat viral infections, but there are a few antiviral drugs used to treat certain viral infections. However, the best treatment for most minor illnesses caused by viruses is often rest and plenty of fluids.
Treatment of infants
For infants, especially those younger than 28 days, your baby might need to be admitted to the hospital for testing and treatment. In babies this young, a fever could indicate a serious infection that requires intravenous (IV) medications and round-the-clock monitoring.
Hygiene – fevers are commonly caused by bacterial/viral infections. Good hygiene practices help reduce the risk of developing an infection. This includes hand washing before and after meals, and after going to the toilet.
A person with a fever caused by an infection should have as little contact as possible with other people, to prevent the infection from spreading. Whoever is caring for the patient should regularly wash their hands with warm soap and water.
You can try a number of things to make yourself or your child more comfortable during a fever:
- Drink plenty of fluids. Fever can cause fluid loss and dehydration, so drink water, juices or broth. For a child under age 1, use an oral rehydration solution such as Pedialyte. These solutions contain water and salts proportioned to replenish fluids and electrolytes. Pedialyte ice pops also are available.
- Rest. You need rest to recover, and activity can raise your body temperature.
- Stay cool. Dress in light clothing, keep the room temperature cool and sleep with only a sheet or light blanket.
In most cases, a fever will come and go without much intervention from a doctor. If a specific cause for fever is found, then the doctor can prescribe the appropriate medication and treat the illness. Occasionally, a second antibiotic, an antifungal medication, or other drug will be needed. Usually, with the appropriate therapy an infection will resolve and the person will return to a normal temperature.
In some cases, a fever can be life-threatening. This is often seen in people with poor immune systems, certain types of meningitis, and severe abdominal pain. Pneumonia with fever can be life threatening in an older person. Any infection in which the source is not found can continue to get worse and become very dangerous. Severe hyperthermia can cause a coma, brain damage, or even death. Usually, if the cause of the fever is diagnosed quickly and treated appropriately, the prognosis is good, but the prognosis is poorer if there are diagnostic and treatment delays and organs become progressively damaged.
Complications of a fever may include:
- Severe dehydration
- Fever-induced seizure (febrile seizure), in a small number of children ages 6 months to 5 years
Febrile seizures usually involve loss of consciousness and shaking of limbs on both sides of the body. Although alarming for parents, the vast majority of febrile seizures cause no lasting effects.
If a seizure occurs:
- Lay your child on his or her side or stomach on the floor or ground
- Remove any sharp objects that are near your child
- Loosen tight clothing
- Hold your child to prevent injury
- Don’t place anything in your child’s mouth or try to stop the seizure
Most seizures stop on their own. Take your child to the doctor as soon as possible after the seizure to determine the cause of the fever.
Call for emergency medical assistance if a seizure lasts longer than 10 minutes.