Apple Watch Series 8’s temperature sensor: How it will work, what it means for women’s health

The Apple Watch Series 8 might not look very different from its predecessor, but it comes with one key new feature: a temperature sensor. Now before you think that the Apple Watch Series 8 can be used to check whether you have a fever, hold on. The temperature sensor–Apple is actually using two sensors for this—is meant for an entirely different purpose: women’s health and given retrospective data on ovulation. Let’s take a look at what this feature is about and what it could mean.
Apple Watch Series 8: Temperature sensor and how it works?
As noted above, Apple is relying on two sensors to measure what is known as the ‘basal body’ temperature. While one sensor is on the back of the watch, and thus nearest the skin, the other is just under the display. Apple says this design is meant to reduce bias from the outside environment which might affect accurate readings.
The temperature sensor cannot be used to just body temperature if you suspect you have a fever. Remember this is not calculated in real-time. The feature is designed to give retrospective data on ovulation and help women understand their menstrual cycle better.

According to Apple, the Watch Series 8 will sample the wr temperature during sleep every five seconds at night. It will be capable of measuring “changes as small as 0.1-degrees Celsius in the body. Women users will be able to see “nightly shifts in baseline temperature.” But Apple also notes that the baseline temperature or basal temperature is also impacted other factors such as fatigue, illness, jet lag or even exercise.
For women, a rise in baseline temperature can be an indicator of ovulation–the fertile period in one’s menstrual cycle. But again, Apple is not giving this data in real-time, rather it is shown retrospectively. For women, who regularly track their cycles, the data could help them understand their cycles better and also get an indication of when ovulation typically occurs for them. According to Apple, “temperature sensing also enables improved period predictions.”

The Cycle Tracking feature in watchOS 9 will also notify women if there is a possible deviation in their cycle such as “irregular, infrequent, or prolonged periods, and persent spotting.” All of these can “be symptoms of underlying health conditions,” according to the company.
What is basal body temperature, and how does it help track Ovulation?
According to the MayoClinic, “basal body temperature is one’s body temperature when one is at rest,” and ovulation may cause a slight increase in this. Ovulation typically begins two-three days before the temperature rises and during ovulation, the rise might be less than ½ degree Fahrenheit.
The idea is that tracking basal temperature could help indicate possible fertility dates and help those who are trying to conceive. Or conversely, ensure that those who do not wish to conceive can take extra other precautions around these particular days. The Mayo Clinic also notes that “the method requires motivation and diligence,” when being used to prevent pregnancy.
How the temperature sensor will work on the Apple Watch Series 8.
Also, there are other factors which impact basal temperature such as illness, fever, stress, shift work, interrupted sleep cycles or oversleeping, alcohol, jet lag, other gynaecological disorders and even medication could impact this negatively.
It is also noted that when using basal temperature tracking methods, it needs to be recorded at the same time, every day as soon as one wakes up. But it looks like the Apple Watch will do this every five seconds at night while one is sleeping. It also means one will have to wear the watch to sleep at night in order to get more accurate results.

Some studies have also shown that it is not a very reliable method to determine ovulation times, given that basal temperature is impacted other factors as we’ve noted above.
Will this new temperature sensor help detect any other issues with menstrual cycles? Can it be used as a form of birth control?
Do note that Apple also notes that the “Cycle Tracking app should not be used as a form of birth control.” It also notes that the data cannot be used to “diagnose a health condition,” say Polycystic Ovary Syndrome (PCOS) and that should ideally be done a doctor. Apple also notes that the “temperature-sensing feature is not a medical device” and “not intended for use in medical diagnosis, treatment, or for any other medical purpose.”
So if you are someone who is say undergoing fertility treatments or worried that you might need them, then the Apple Watch Series 8 and its data alone is not enough to help with these. It should also be noted that Apple is only showing ovulation data retrospectively. The data can give broader indications of one’s menstruation cycle.