Fever describes a rise in a person's body temperature. It may be caused by many different viral and bacterial infections, or other medical conditions.
Fever is one of the most common symptoms of illness that can range from benign to potentially serious. Many infants and children develop high fevers in response to minor viral illnesses.
As a person develops a fever, he or she may actually feel cold despite the rise in body temperature. Once the body temperature has increased to a stable level, the person may then feel the onset of warmth, flushing or sweating.
What temperature is a fever?
A child has a fever when the temperature is at or above one of these levels:
- 100.4 °F (38 °C) measured rectally
- 99.5 °F(37.5 °C) measured orally (in the mouth)
- 99 °F (37.2 °C) measured under the arm
An adult probably has a fever when his or her temperature rises above 99 - 99.5 °F (37.2 - 37.5 °C), depending on the time of day.
Causes of Fever
- Viral and Bacterial Infections. Many types of infections can cause a fever, including colds, influenza (flu), strep throat, ear infections (otitis media), pneumonia, urinary tract infections (UTIs), gastroenteritis, bone infections (osteomyelitis), appendicitis and meningitis.
- Childhood Immunizations. Children may develop a low-grade fever for 1-2 days after some immunizations, such as the DTaP vaccine.
- Autoimmune disorders. Autoimmune disorders, such as rheumatoid arthritis, lupus and vasulitis, may also cause fevers.
- Medications. Fever may also be the first symptom of some forms of cancer, such as Hodgkin's disease, non-Hodgkin's lymphoma, and leukemia
Effects of Fever
Some children may develop seizures in response to high fevers. These are called febrile seizures. Most febrile seizures end quickly and do not cause any permanent damage and do not mean that the child will develop epilepsy.
Brain damage from a fever generally will not occur unless the fever is over 107.6 °F (42 °C). Untreated fevers caused by infection will seldom go over 105 °F unless the child is overdressed or trapped in a hot place.
When to Contact a Medical Professional About Fever
Children with Fever
Call a doctor right away if your child:
- Is younger than 3 months old and has a rectal temperature of 100.4 °F (38 °C) or higher
- Is 3 -12 months old and has a fever of 102.2 °F (39 °C) or higher
- Is under age 2 and has a fever that lasts longer than 24 - 48 hours
- Is older and has a fever for longer than 48 - 72 hours
- Has a fever over 105 °F (40.5 °C), unless it comes down readily with treatment and the person is comfortable
- Has other symptoms that suggest an illness may need to be treated, such as a sore throat, earache, or cough
- Has been having fevers come and go for up to a week or more, even if they are not very high
- Has a serious medical illness, such as a heart problem, sickle cell anemia, diabetes, or cystic fibrosis
- Has a new rash or bruises appear
- Has pain with urination
- Has trouble with the immune system (chronic steroid therapy, after a bone marrow or organ transplant, spleen was removed, is HIV-positive, or is being treated for cancer)
Call 911 if you or your child has a fever and:
- Is crying and cannot be calmed down
- Cannot be awakened easily or at all
- Seems confused
- Cannot walk
- Has difficulty breathing, even after their nose is cleared
- Has blue lips, tongue, or nails
- Has a very bad headache or stiff neck
- Refuses to move an arm or leg
- Has a seizure
Adult with Fever
Call your doctor right away if you are an adult and you:
- Have a fever over 105 °F (40.5 °C), unless it comes down readily with treatment and you are comfortable
- Have a fever that stays at or keeps rising above 103 °F
- Have a fever for longer than 48 - 72 hours
- Have had fevers come and go for up to a week or more, even if they are not very high
- Have a serious medical illness, such as a heart problem, sickle cell anemia, diabetes, cystic fibrosis, COPD, or other chronic lung problems
- Have a new rash or bruises appear
- Have pain with urination
- Have trouble with your immune system (chronic steroid therapy, after a bone marrow or organ transplant, had spleen removed, HIV-positive, were being treated for cancer)
- Have recently traveled to a third world country
Home Care for Fever
No treatment is necessary in older children and adults if the fever is mild and there are no other problems. Treatment should focus on staying rested and drinking fluids.
The illness is probably not serious if your child:
- Is still interested in playing
- Is eating and drinking well
- Is alert and smiling at you
- Has a normal skin color
- Looks well when their temperature comes down
Take steps to lower a fever if you or your child is uncomfortable, vomiting, dried out (dehydrated), or not sleeping well. The goal is to lower, not eliminate, the fever.
When trying to lower a fever:
- Remove excess clothing or blankets. The room should be comfortable, not too hot or cool. Try one layer of lightweight clothing, and one lightweight blanket for sleep. If the room is hot or stuffy, a fan may help.
- A lukewarm bath or sponge bath may help cool someone with a fever. This is especially effective after medication is given -- otherwise the temperature might bounce right back up.
- Do NOT use cold baths, ice, or alcohol rubs. These cool the skin, but often make the situation worse by causing shivering, which raises the core body temperature.
Here are some guidelines for taking medicine to lower a fever:
- Acetaminophen (Tylenol) and ibuprofen (Advil, Motrin) help reduce fever in children and adults. Sometimes doctors advise you to use both types of medicine.
- Take acetaminophen every 4 - 6 hours. It works by turning down the brain's thermostat.
- Take ibuprofen every 6 - 8 hours. DO NOT use ibuprofen in children younger than 6 months old.
- Aspirin is very effective for treating fever in adults. DO NOT give aspirin to a child unless your child's doctor tells you to.
- Know how much you or your child weighs, and then always check the instructions on the package.
- In children under age 3 months, call your doctor first before giving medicines.
- Eating and drinking with a fever:
- Everyone, especially children, should drink plenty of fluids. Water, popsicles, soup, and gelatin are all good choices.
- Do not give too much fruit or apple juice and avoid sports drinks in younger children.
- Although eating foods with a fever is fine, do not force foods.
What to Expect at Your Office Visit
Your doctor will perform a physical examination to look for signs of infection or other possible causes of the fever.
Your doctor will recommend treatment depending on the duration and cause of the fever, as well as other symptoms.
In some cases, tests may be ordered to identify the cause of the fever. Tests may include blood tests (CBC), urinalysis (UA), or chest x-ray.