Body temperature is often thought of as a fixed number, but that’s not entirely true. While we commonly hear that normal body temperature is 98.6°F (37°C), this is only an average. Your actual body temperature can vary, and that's completely normal.
“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 temperature can fluctuate within this range throughout the day due to various factors and it’s still considered normal.
Factors that influence body temperature changes
Body temperature doesn’t remain constant throughout the day. Your temperature may change for several reasons:
- Time of day: It’s normal for your temperature to be at its lowest point just before you wake up and highest about an hour before you go to bed.
- Physical activity: When you exercise or engage in any physically demanding activity, your body generates heat, which can cause your temperature to rise.
- Hormonal fluctuations: Women of childbearing age experience changes in body temperature throughout their menstrual cycle. Temperature tends to be lower in the first half of the cycle and rises during ovulation.
- Diet: Eating spicy foods can trigger your brain to think that your body is overheating, causing sweating and a temporary drop in body temperature.
- Gender: Women have slightly higher body temperatures compared to men.
- Age: Younger people tend to have higher body temperatures than older adults.
- Body weight: People with a higher body weight may have a higher body temperature than those with a lower body weight.
When to be concerned about high body temperature
A body temperature above 100.4°F is considered a low-grade fever, while a temperature above 103°F is considered a high-grade fever. Most low-grade fevers resolve within a few days.
If your fever is accompanied by symptoms like a rash, severe pain or respiratory issues, you should reach out to your health care provider. Otherwise, rest and stay hydrated.
“We often think of temperatures as fevers and think of them as a sign of an infection,” Dr. Pero said. Other causes of elevated temperature include:
- Heat exhaustion
- Serious sunburn
- Inflammatory medical conditions, such as rheumatoid arthritis
- Overactive thyroid
When to be concerned about low body temperature
A body temperature below 95°F (35°C) is abnormally low and is classified as hypothermia, a serious condition that can result from exposure to cold weather or wet clothing. Hypothermia is a medical emergency and requires immediate attention. Signs of hypothermia include shivering, confusion and loss of coordination. If someone's rectal temperature or oral temperature drops below 95°F, seek medical help immediately and call 911.
Low body temperature can also occur in certain medical conditions, such as an underactive thyroid or spinal cord injuries. Symptoms of hypothermia may develop slowly, and the temperature measured with a thermometer can help identify the severity of the condition.
Signs and symptoms of hypothermia
Recognizing the signs and symptoms of hypothermia can be lifesaving, especially in cold environments. These symptoms may include:
- Intense shivering
- Slurred speech
- Drowsiness
- Confusion
- Weak pulse
It’s essential to address hypothermia quickly by moving the person out of the cold, removing wet clothing and covering them with warm blankets. Call 911 immediately if the person’s condition worsens or they are unresponsive.
When to seek medical care
Extremely high or low body temperatures should be taken seriously and may indicate an underlying condition or environmental exposure to extreme temperatures. High body temperature, especially when associated with symptoms like dizziness, nausea or heatstroke, should prompt medical evaluation. Similarly, low body temperature, especially when exposed to cold weather for extended periods, can be a sign of hypothermia, which requires urgent care.
If you are experiencing unexplained fluctuations in your body temperature along with other symptoms like pain, weight changes or appetite loss, it’s important to talk to your health care provider. If you notice symptoms of hypothermia or a high fever that won’t subside, it’s a good idea to get help right away.
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). Any unusual changes in these areas may indicate a medical issue that should be discussed with your doctor.
The bottom line
Fluctuations in body temperature are normal, but temperatures that are too high or too low may signal a medical emergency. If you experience these extremes, especially with other symptoms, contact a health care professional or call 911. Reach out to Banner Health if you would like to connect with a health care professional.
Other useful articles
- Fevers at Every Age
- Why Your Heart Rate Goes Up When You’re Sick
- 3 Essential Things You Need to Know About Frostbite This Winter
Content in this article was updated on October 9, 2024.
