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Why Oura Measures Temperature from Your Finger

The term “body temperature” is often used to describe methods of measuring temperature interchangeably without clarifying that different measurement sites yield different insights. Your body is typically divided into two regions – your core and your “shell” (including your skin and extremities). 

Your body is always trying to maintain an ideal temperature range in your core which means it prioritizes stabilizing your internal temperature while the range of your shell fluctuates more widely. For example, your core body temperature might be relatively stable while your skin temperature changes based on your environment and your body’s internal adjustments to make you hotter or colder.  

As a result, where you measure your temperature from is key based on your goal: are you trying to capture your core body temperature or fluctuations in your shell? It’s important to remain consistent, regardless of what you measure. 

Your Shell Shows More Temperature Variation

Your core body temperature is the clinical standard (the most well studied). It’s what doctors try to measure when checking for fertility or infection. However, outside of a doctor’s office or lab, its most common measurement sites (e.g., mouth, armpit, or rectum) can lack practicality, especially for continuous measurements.

On the other hand, your shell temperature is less invasive to measure and can provide insights on the same rhythms as core temperature—menstrual cycles, daily fluctuations, circadian rhythms, etc.—as well as other health indicators like a fever. Your shell temperature can easily be measured from easily accessible external locations like your forehead or hands.

New research is starting to show that shell temperature can even carry more information than core temperature due to your body’s insulation—resulting in limited changes in core temperature. Shell temperature represents a unique opportunity to capture information about any subtle or rapid changes in temperature. Your shell exhibits more frequent, and larger, changes in your skin temperature, while core changes can be more muffled.  

With this in mind, Oura measures body temperature directly from the skin of your finger picking up on these subtle variations and providing a comfortable, easy way to continuously measure your temperature without disrupting your routine. The ring itself has three negative temperature coefficient (NTC) sensors that can detect changes as small as 0.05° celsius. 

Your Skin Temperature Can Change Independently or With Your Core Body Temperature

Your body is constantly making adjustments to keep up with how your external environment and internal changes are influencing your core temperature. One of your body’s strongest tools is using blood to move heat to or from your core—helping maintain your ideal temperature. 

As a result, sometimes your shell and core temperature move together, while other times they change in opposite directions. 

Your shell often indicates what’s happening inside your core. For example, if your body is trying to cool itself before bed, your core temperature will decrease as your skin temperature goes up—a sign of heat being vented through your extremities. The opposite is true as well – if you head outside in the winter and find that your fingers and toes get cold first, your body is trying to control it’s core temperature by pulling heat to your center. 

Other times, your core and shell temperature will change together. For example, they may both rise in cases of a fever or after ovulation. 

How Oura Mesures Your Body Temperature

Oura prioritizes accuracy when it reads and reports your body temperature: 

  • Direct Skin Temperature: Oura is one of the few wearables that continuously measures body temperature directly from your skin rather than estimating it using your external environment. At night, your skin temperature is closely related to your internal temperature and does not require an invasive thermometer to read. This allows for continuous monitoring each night, without disrupting the user’s lifestyle. 
  • Relative Values: Oura shows your body temperature in relation to your personal baseline. For example, rather than display your temperature as 36.5 °C / 99.5 °F, Oura will show how much higher or lower your temperature is than your baseline (+0.1 °C/°F). 
  • Strain vs. Recovery: To provide you with meaningful insights, Oura exclusively reports your nighttime body temperature. Body temperature is a well-regulated measurement that can be influenced by daytime habits. Measuring at night is the best way to keep conditions stable in order to reveal an accurate picture of your recovery.
  • Sampling Rate: Every minute, Oura’s temperature sensor measures your body’s skin temperature. Our algorithm selects values that are most likely to correlate with core body temperature and averages across those data points to provide you with a single value that best represents your night.

If you’re interested in learning how to interpret your body temperature data, read more about your graphs and values or which temperature patterns matter.

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