Your body has an internal thermostat and it aims to maintain your temperature as close to your goal as possible. The stability of that number, known as your core body temperature, reflects your body’s ability to turn up the heat or cool things down to keep you within your ideal range.
Each day, your body has plans to adjust your temperature to follow your circadian rhythm by warming you up to start the day and cooling you down for sleep. Yet diet, exercise, hormones, and many other things affect your temperature. As a result, your body is constantly making adjustments to keep it all balanced:
The stability of your temperature is an indicator of your body’s ability to adjust in the face of challenges. It signals how you’re recovering, how prepared you are for the day, if you’re coming down with an illness, or if hormones in your body are hard at work.
On average, an individual’s core body temperature varies from 36.5–37.5 °C (97.7–99.5 °F) over the course of a day. Your body temperature doesn’t remain constant, however, it fluctuates according to your circadian rhythm.
Generally, this means your body temperature is at its lowest a few hours before you wake and its highest an hour or two before bed.
An individual’s core body temperature typically changes by about 1 °C (1.8 °F) between its highest and lowest points each day. Anything outside of that range indicates that something is challenging your body and preventing it from adjusting.
At the surface of your skin, where heat from your blood and cold from the environment are more intermingled, the range is typically much larger.
Your skin temperature and core temperature can even change in opposite directions throughout the day. For example, if your core temperature is too high, your body tries to cool itself by pushing blood to the skin so it can shed that excess heat. But in the case of fever, or after ovulation, both will rise similarly.
With all of these changes, it’s important to keep in mind where you’re measuring from before you compare numbers.
During the day, your temperature varies as you move, eat, drink, socialize, and change your environment. Because there is so much variation in temperature throughout the day, if you want to measure your overall health status, it’s best to measure your temperature at night when your body is stable.
At night, your body’s temperature is a reflection of what happened during the day—is your body stressed outside of its ideal range or is it able to maintain your stable thermostat?
If your body temperature is outside of your normal range, your body is signaling to you that something is pushing it beyond what it can adjust for.
Look for these patterns in your nightly core temperature:
Your circadian rhythm helps your body move between being awake or asleep. As part of this rhythm, your core body temperature drops near your optimal bedtime and rises again just before you wake up. Keep in mind that melatonin release helps trigger your body’s cooling process and may be easily disrupted by blue light.
If your average temperature is significantly higher or lower than average, or if it fails to change when you try to go to sleep, then your body may be stuck under strain—preventing it from flexibly adjusting throughout the night. If you fall asleep at a different time than you normally do (e.g., traveling to a new time zone) your temperature rhythms may also be misaligned.
If you’re getting sick, even before you get a fever, your body’s temperature may rise. While estimates vary, normal daily temperature fluctuation is around 1 °C (1.8 °F). If you spot a high temperature outside of that range, it may mean your body is fighting to keep you healthy. Some illnesses may even cause a fever. Regardless, a positive sign of recovery is your temperature returning to normal afterward.
Powering your organs can generate a lot of internal heat. If you have a large meal or a few drinks close to bed, you may find that your temperature remains elevated throughout the night. This is evidence that your digestive system is working overtime.
You may spot changes around 0.5 °C (0.9 °F). Being in touch with your body can help you identify if overheating is due to something you can control (e.g., mealtimes or bedding) or is the result of another bodily change (e.g., hot flashes or melatonin).
If you track your menstrual cycle, you may see your temperature range shift with your hormones. This usually results in lower body temperatures during the first half of the menstrual cycle (follicular phase), followed by a rise in the second half (luteal phase). Note that using hormonal birth control may suppress monthly temperature variation and/or increase your average temperature.
You have the power to influence your body temperature more than you might think. There are even Tibetan monks who meditate and raise their skin temperature high enough to dry a wet towel resting on their backs. We recommend starting with some of these simpler hacks:
Observing your body’s day-to-day temperature can inform you. Start monitoring your trends and see what patterns emerge.