A fever is defined as an elevated body temperature, measured at or above 100.4°F (38°C) when taken orally. This temperature increase is a physiological response, indicating the immune system is actively engaged in fighting off an infection. The fever is a symptom, not a disease, representing the body’s attempt to create an environment less favorable for pathogens like viruses or bacteria. Knowing the expected duration of a fever helps determine when this common symptom requires professional medical evaluation.
Typical Duration for Common Fevers
Most fevers associated with routine, self-limiting illnesses resolve quickly. For the common cold, influenza, or minor viral infections, the elevated temperature usually lasts between 24 and 72 hours, signaling that the body’s immune defenses are effectively neutralizing the infectious agent.
The fever pattern during this time is often intermittent, spiking and then returning closer to normal, sometimes with the assistance of medication. This fluctuation is a normal part of the body’s process as it adjusts the internal thermostat in response to the infection. A fever that subsides completely within three days is considered acute and follows the expected timeline for common infections.
Duration Thresholds That Require Medical Attention
The duration of an elevated temperature is a primary indicator for seeking professional medical advice. For adults and older children, a fever lasting more than 72 hours (three full days) warrants consultation with a healthcare provider. A persistent fever suggests the underlying cause may be more complex or that the body is struggling to overcome the infection.
Specific age groups have much lower thresholds for concern. In infants younger than three months, any temperature of 100.4°F (38°C) or higher requires immediate medical evaluation, regardless of duration. For children between three and 24 months, a fever lasting more than 24 to 48 hours without an obvious cause should prompt a call to the doctor. These shorter timeframes exist because young children are more vulnerable to serious, rapidly progressing infections.
Factors That Influence How Long a Fever Lasts
The duration of a fever depends significantly on the underlying cause. Fevers caused by common viruses, such as those responsible for colds or minor gastrointestinal infections, tend to be shorter, often lasting only a day or two. Conversely, fevers resulting from bacterial infections, like strep throat or pneumonia, frequently persist until the infection is treated with appropriate antibiotics.
The patient’s age and overall immune status also play a substantial role. Infants and the elderly may exhibit different response times; the elderly sometimes display a blunted fever response, while infants’ fevers are concerning due to the risk of rapid deterioration. Individuals with compromised immune systems, such as those undergoing chemotherapy, may experience fevers that last longer because their bodies take more time to mount an effective defense.