Average Body Temperature: What's Normal

Man sick with fever reading thermometer
What is considered average body temperature, what is considered a fever and why is it that our body temperature seems to fluctuate day-to-day and even hour-by-hour? Julia Jenkins, DO, UnityPoint Health, answers some common questions.

What is Normal Body Temperature?

Historically, normal body temperature has been known to be 98.6 degrees Fahrenheit. In reality, normal body temperature is actually more of a range, likely between 97 and 100-degrees Fahrenheit. There are recent studies that suggest the average body temperature is trending down over time and is likely closer to 98 degrees Fahrenheit for the general population.

Most adults don’t need to monitor their body temperature with any regularity. The body regulates it all on its own through a well-functioning immune and inflammatory system.

What Temperature is Considered a Fever?

In medicine, 100.4 degrees Fahrenheit is considered high body temperature, also known as “having a fever.” If your body temperature is over that threshold, it may mean your immune system has been activated to fight off an infection. If you do get a temperature reading of greater than 100.4, you should be vigilant and limit your exposure to others.

A fever is often accompanied by other signs and symptoms that suggest infection, including:

  • Shivering (chills)
  • Headache
  • Not feeling hungry (loss of appetite)
  • Body aches
  • Sweating

What If I Have a High Body Temperature, But Don’t Feel Sick?

There are a lot of isolated things that can cause an increase in body temperature, but your body is very good at regulating and returning the body temperature to a normal range. If you have an elevated body temperature and you do not feel ill, that is not necessarily a reason to be concerned. In this case, it’s a good idea to re-check your temperature about an hour after the high reading to see if it has returned to normal. Also, watch more closely for signs of illness.

Outside of Illness and Infection, What Can Cause High Body Temperature?

  • Warm/Cold weather. External factors, like warm summertime weather or chilly winter weather, can alter the core body temperature. Your level of activity, current health status and conditions of exposure will all play a significant role in exactly how much it causes your body temperature to change.
  • Hot showers. Just like hot weather, hot showers can impact your body temperature. For an accurate reading using a thermometer, wait 60 minutes after showering to check your temperature. Similarly, cold showers can bring your body temperature down.
  • Hot food & drinks. If you are checking your temperature using an oral thermometer in your mouth, wait 15-20 minutes after eating or drinking. Oral intake does not impact core body temperature but can cause a false reading on your thermometer.
  • Laying on one side. Theoretically, if you use an ear thermometer right after waking, you could have a slightly higher body temperature on the side you slept on. If so, recheck about an hour after waking.
  • Teething in children. Teething may cause a very slight increase, but it will not cause a fever. If your baby is teething and has a fever over 100.4, it’s likely due to an illness.
  • Pregnancy. Many women will feel warm during the early stages of pregnancy. This change in temperature is usually minimal and wouldn’t be considered a fever. This rise in temperature is due to increased blood volume, hormone changes and other physiological aspects supporting the growing fetus.
  • Gender. Men and women have very similar core body temperatures. There can, however, be a difference in skin temperature and perceived warmth. Women tend to feel comfortable in slightly warmer environments. The explanation is actually very complicated – but in general, think of it being related to hormones and metabolic rate. Men have a higher metabolic rate and higher muscle mass and thus are a bit warmer.
  • Stress. Chronic stress and significant emotional incidents can both cause the body temperature to increase – likely due to the body’s inability to efficiently regulate. Chronic stress places demand on the body and can show an increase in body temperature of up to 100 degrees Fahrenheit. Certain short-term, stressful events can be more dramatic with spikes of body temperature of up to 105 or even 106 degrees Fahrenheit. This is likely due to a physiological response, like the “fight or flight” response.
  • Weight gain. During times of weight loss, you’ll notice a drop in average body temperature over time that’s due to less calorie intake and decreasing metabolic rate. If you gain the weight back, the body temperature will rise again.

Is There a Best Time of the Day to Take a Temperature?

Body temperature varies throughout the day and is lowest in the morning and highest in the afternoon. Your body has a complex thermoregulation mechanism to help keep its temperature within the normal ranges. There really isn’t a “best time of day” to check your temperature. Even within the normal daily fluctuations, it would be uncommon for a person to have a temperature more than 100.4 degrees Fahrenheit without some secondary cause – like illness.

What Type of Thermometer is Best?

Digital thermometers are generally accurate and safe for most ages. To get an accurate reading for babies under 3 months old, it’s best to use a rectal temperature. Mouth and ear thermometers are not recommended for this young age group. Forehead thermometers are also accurate and recommended. They generally are quick, and well tolerated, but the drawback is they are more expensive. It’s also not a good idea to use those plastic strip thermometers that look like stickers. They are not accurate.

What are Ways to Bring Your Body Temperature Down?

Whether you have fever from an illness, or you are simply seeing a temporary body temperature spike, it’s important to give your body the tools it needs to cool down. Here are some non-medicinal things you can try:

  • Move to a cooler, indoor room
  • Take off clothing
  • Use a cool compress – like cold wash cloth on the forehead
  • Take a cool shower/bath