A fever is when your body temperature rises higher than normal. A fever itself isn’t an illness. Rather, it’s a symptom of a wide range of health conditions. When your body temperature rises a few degrees above normal, it can be a sign that your immune system has been activated, often to fight an infection. It can also be a side effect of some medications and vaccinations.

What is considered a fever?

Common knowledge states that a “normal” body temperature is 98.6 degrees Fahrenheit (37 degrees Celsius). But your baseline body temperature may vary by a degree or more. It also fluctuates. It’s typically lower in the morning and higher in the evening. It’s higher during certain points of your menstrual cycle and when you’re exercising.

Infants and young children normally have slightly higher body temperatures than older children and adults. So infants and younger children have slightly higher fever temperatures.