Many viral illnesses, especially the flu, can cause fevers of 102°F (39°C) or higher for up to 48 hours.

If you do not have other symptoms, a fever of 102°F (39°C) or less that lasts 3 to 4 days is usually not a cause for concern.

Ongoing fevers

You may need to see a health professional to determine what is causing your fever in the following situations:

• Adults older than 60 may have an increased risk for a more serious problem if a fever higher than 100°F (37.8°C) does not go away after 2 full days of home treatment.
• A fever that occurs after an operation or other medical procedure may be caused by an infection.
• An ongoing fever that does not get better with home treatment may mean you have a more serious illness, such as a bacterial infection.
• A fever develops in anyone who has certain health risks.
• A fever without an obvious cause lasts longer than 4 full days.
• A fever without an obvious cause comes back more than once within 3 weeks.
• A recurrent or ongoing fever develops within 6 weeks of travel outside your country.

Recurrent fevers are those that occur 3 or more times within 6 months and are at least 7 days apart. If you have frequent or recurrent fevers, it may be a symptom of a more serious problem. Talk to your doctor about your fevers.

Remember, fever is only a symptom. Often the importance of a fever can only be determined when other symptoms are considered. A careful evaluation of your health may help you identify other symptoms that may be related to the fever.