Your body’s like a little furnace. It puts out heat all the time. It comes from your body doing the work that keeps you alive. When it puts out a lot more or a lot less heat than usual, it’s trying to tell you there’s a problem.

Not everyone’s “normal” body temperature is the same. Yours could be a whole degree different than someone else’s. A German doctor in the 19^thcentury set the standard at 98.6 F, but more recent studies say the baseline for most people is closer to 98.2 F.

For a typical adult, body temperature can be anywhere from 97 F to 99 F. Babies and children have a little higher range: 97.9 F to 100.4 F.

Your temperature doesn’t stay same all day, and it will vary throughout your lifetime, too. Some things that cause your temperature to move around during the day include:

• How active you are
• What time of day it is
• Your age
• Your sex
• What you’ve eaten or had to drink
• (If you’re a woman) where you are in your menstrual cycle

Your temperature reading changes based on where on your body you measure it. Underarm readings can be a degree lower than what you’d find from your mouth. Rectal temperatures usually are up to a degree higher than mouth readings.

A body temperature higher than your normal range is a fever. It’s hypothermia when the body temperature dips too low. Both need to be watched.

How high is too high when it comes to your temperature? Anything above 100.4 F is considered a fever. You may feel terrible, but on the whole, a fever isn’t bad for you. It’s a sign your body is doing what it should when germs invade. It’s fighting them off.

However, if your temperature is 103 F or higher or if you’ve had a fever for more than 3 days, call your doctor. Also call if you have a fever with symptoms like severe throat swelling, vomiting, headache, chest pain, stiff neck or rash.

For children, fevers are a bit more complicated. Call your pediatrician if your child is:

• Under 3 months and has a rectal temperatures of 100.4 F or higher
• Between 3 months and 3 years and has a rectal temperature over 102 F
• Older than 3 years and has an oral temperatures above 103 F
• Between 3 and 6 months and — along with a fever — is fussier or more uncomfortable than usual, or doesn’t seem alert
• Sick enough for you to be concerned, regardless of what the thermometer says