Normal body temperature may change during any given day. It is usually highest in the evening. Other factors that may affect body temperature are:
In the second part of a woman's menstrual cycle, her temperature may go up by 1 degree or more.
Physical activity, strong emotion, eating, heavy clothing, medications, high room temperature, and high humidity can all increase your body temperature.
Fever is an important part of the body's defense against infection. Most bacteria and viruses that cause infections in people thrive best at 98.6 °F. Many infants and children develop high fevers with minor viral illnesses. Although a fever signals that a battle might be going on in the body, the fever is fighting for the person, not against.
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.
Febrile seizures do occur in some children. However, most febrile seizures are over quickly, do not mean your child has epilepsy, and do not cause any permanent harm..
Unexplained fevers that continue for days or weeks are called fevers of undetermined origin (FUO).
Almost any infection can cause a fever. Some common infections are:
Medications, such as some antibiotics, antihistamines, and seizure medicines
A simple cold or other viral infection can sometimes cause a high fever (102 - 104 °F, or 38.9 - 40 °C). This does not usually mean you or your child have a serious problem. Some serious infections may cause no fever or even a very low body temperature, especially in infants.
If the fever is mild and you have no other problems, you do not need treatment. Drink fluids and rest.
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. Remember, the goal is to lower, not eliminate, the fever.
When trying to lower a fever:
Do NOT bundle up someone who has the chills.
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.
When to Contact a Medical Professional
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
Recently had an immunization
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)
Has recently traveled to a third world country
Call 911 if you or your child has a fever and:
Is crying and cannot be calmed down (children)
Cannot be awakened easily or at all
Has difficulty breathing, even after their nose is cleared
Has blue lips, tongue, or nails
Has a very bad headache
Has a stiff neck
Refuses to move an arm or leg (children)
Has a seizure
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
What to Expect at Your Office Visit
Your doctor will perform a physical examination, which may include a detailed examination of the skin, eyes, ears, nose, throat, neck, chest, and abdomen to look for the cause of the fever.
Treatment depends on the duration and cause of the fever, as well as your other symptoms.
Leggett J. Approach to fever or suspected infection in the normal host. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 288.
Neil K. Kaneshiro, MD, MHA, Clinical Assistant Professor of Pediatrics, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.