What is a fever?
A fever is when your body temperature rises above normal, usually 100.4°F (38°C) or higher. It’s not an illness on its own, but a signal that your body is responding to something—often an infection.
In many cases, a fever is part of your body’s natural defense system. It can also happen after exercise, exposure to heat, or certain vaccinations.
Common causes of fever include:
- Viral infections like colds or the flu
- Bacterial infections
- Reactions to medications or vaccines
- Heat exposure or dehydration
- Inflammatory conditions in the body
Symptoms
A fever can feel different from person to person. Along with a higher temperature, you may notice other changes in how you feel.
Common symptoms include:
- Feeling warm or having chills
- Headache
- Muscle aches or fatigue
- Loss of appetite
- Nausea or stomach upset
- Sweating or flushed skin
In young children, a rapid rise in temperature can sometimes lead to a brief seizure.
How is it diagnosed?
The most reliable way to confirm a fever is by taking a temperature with a thermometer. Digital thermometers are commonly used and can measure temperature by mouth, under the arm, or rectally.
For infants and very young children, rectal measurements provide the most accurate results. Your provider may also ask about symptoms and perform an exam to understand what’s causing the fever.
How is it treated?
Treatment focuses on helping you feel more comfortable while your body recovers.
At-home care often includes:
- Rest and plenty of fluids
- Fever-reducing medications like acetaminophen or ibuprofen
- Light clothing and a comfortable room temperature
A lukewarm bath may also help lower body temperature. Aspirin should never be given to children or teens due to the risk of serious complications.
Most fevers improve within a few days. However, medical care is important if symptoms worsen, last longer than expected, or occur in infants younger than 3 months.
