You might have heard that normal body temperature is 98.6°F (37°C). But that’s not entirely true.
“Normal adult body temperature ranges from 97°F to 99°F,” said Lurlyn Pero, MD, an internal medicine specialist at Banner Health Center in Phoenix, AZ. Your average body temperature can fluctuate within that range and still be considered normal.
Here’s what could be behind normal differences in body temperature
Your body temperature might rise or fall for several reasons:
- It’s normal for your temperature to be lowest before you wake up, and highest about an hour before bedtime.
- When you exercise, or you’re physically active, you generate body heat and your temperature will rise.
- Women of childbearing age will have a lower temperature in the first half of their cycle and a rise in temperature when they ovulate.
- Eating spicy foods can send a message to your brain that your body is overheated, which can make you sweat and lower your body temperature.
- Women tend to have higher body temperatures than men.
- Younger people tend to have higher body temperatures than older people.
- People with higher body weight tend to have higher temperatures than people with lower body weight.
Here’s when you should be concerned about high body temperature
A body temperature above 100.4°F is considered elevated, or a low-grade fever. A temperature above 103°F is considered a high-grade fever, Dr. Pero said. Most illnesses that cause low-grade fevers run their course in a couple of days. Talk to your health care provider if you have a rash, severe pain or respiratory symptoms along with your fever. Otherwise, you can rest and stay hydrated while you wait for it to subside.
“We often think of temperatures as fevers and think of them as a sign of an infection,” Dr. Pero said. But other factors can cause high body temperatures:
- Heat exhaustion
- Serious sunburn
- Medical conditions that cause inflammation, such as rheumatoid arthritis
- Medical conditions that increase the body’s metabolism, like an overactive thyroid
Here’s when you should be concerned about low body temperature
A body temperature below 95°F (35°C) is considered abnormally low. Exposure to cold weather or extreme cold can cause low body temperature. It can also be caused by medical conditions such as an underactive thyroid or parathyroid or by spinal cord injuries.
Here’s when you should seek medical care
Extremely high or low body temperature should be treated as an emergency, Dr. Pero said. When your body temperature is too high or too low, it’s usually a sign of illness or exposure to extreme heat or cold temperatures.
If you aren’t feeling well, you’re in pain, or you’re noticing changes in your weight or appetite along with changes in your body temperature, you should talk to your health care provider. You may also want to connect with your health care provider if you notice changes in your body temperature you can’t explain.
Dr. Pero recommends that, along with your body temperature, you monitor four additional vital signs that measure your health—blood pressure, weight, heart rate and respiratory rate (breaths per minute). If you notice any unexplained changes in your vital signs, talk to your health care provider.
The bottom line
It’s normal for your body temperature to fluctuate a bit. But when your body temperature is too high or too low, you should seek medical care. Reach out to Banner Health if you would like to connect with a health care professional.
