Something shifts inside women between the ages of 18 and 42.
Specifically. Their resting body temperature. It goes up. A fraction of a degree. Year after year. The reasons behind it are still foggy, but the trend is undeniable.
Marie Gombert-Labbedens from SRI International in California sees opportunity in this data. Heat isn’t just heat.
“We think there is a lot of information in the temperature signal.”
She thinks wearables might become tools for tracking how fast we age, spotting perimenopause, or flagging health issues before symptoms appear.
Here’s where the data came from. A 1990 study. More than 750 women. They checked their oral or rectal temperatures every morning before getting out of bed. Standard stuff.
The baseline is familiar. Fertility trackers have known this for a while. Temps are lower in the first half of the menstrual cycle. Then they jump after ovulation. The second half runs hotter.
But Gombert-Labedbedens looked closer. She ignored the cycle phases for a second. She looked at age.
Every year. From 18 to 42. Participants got warmer.
By the time a woman hits 35 or older? She averages 0.05°C warmer than her younger counterpart. This holds true for both halves of the cycle.
Does it fit the pattern? Yes. The same team looked at smart ring data recently. Women aged 42 to 53 had warmer skin on their fingers compared to the 18-35 crowd. Continuous tracking. Same result.
So. Why?
Gombert-Labedbens guesses it’s hormonal. Something about the waning reproductive years. Perimenopause hits differently. Suddenly temps spike. Hot flashes. Night sweats. But she notes it’s unclear if these sudden blasts come from the same mechanism as the slow, steady crawl we see now.
The sample set has holes. Big ones. No women on hormonal contraception were included. No women with hormonal conditions like PMOS (formerly known as PCOS). So the story isn’t finished. We don’t know how the pill or syndrome alters this warming trajectory.
Eventually the heat fades. Research shows post-menopause temps drop back down. They level out. They end up looking a lot like male body temperature averages.
Is that why middle-aged women complain less about the cold? Maybe. Anecdotally, they claim to tolerate the chill better.
“We speculate that higher temperature could influence perception.”
It might just feel less severe to a warmer engine.
Smart rings are getting popular. People are wearing them. The data is coming in. The potential is there to map these individual heat trends. Spotting menopause on the horizon? Estimating biological aging rates? Catching ovarian cancer early?
All possibilities.
At least, that’s what Gombert-Labebens hopes. The technology is ready. The biology is complex.
The signal is there.
Whether we know how to listen remains to be seen. 🌡️
