A woman’s resting body temperature gradually increases from age 18 to 42, though the cause remains unclear. This significant finding suggests that temperature-sensing wearables might be utilized for tracking aging, identifying perimenopause, and detecting possible health issues.

“We believe that temperature signals hold valuable health information,” states Marie Gombert-Labedens from SRI International, a California-based research institute. “We aspire to inspire research that identifies new health markers, using this data as a previously untapped resource.”

In 1990s research, Gombert-Labedens and her team studied over 750 women aged 18 to 42 who measured their oral or rectal temperature daily upon waking.

The analysis revealed that participants had lower body temperatures during the initial half of their menstrual cycle and higher temperatures during the latter half when ovulation occurred. This temperature increase is commonly used by many fertility tracking apps to predict the fertile window.

Upon further examination of age-related body temperature fluctuations during various menstrual stages, the researchers discovered that on average, participants’ temperatures increased slightly each year from ages 18 to 42. Notably, women over 35 recorded temperatures approximately 0.05°C higher than younger counterparts across both phases of the menstrual cycle.

Subsequently, the finger skin temperature continuously recorded by smart rings indicates that women aged 42 to 55 exhibit higher temperatures compared to those aged 18 to 35.

Further research is essential to clarify the reasons behind this increase in body temperature, with Gombert-Labedens suggesting it could be linked to hormonal changes, particularly as reproductive years close. During perimenopause, rapid body temperature rises can lead to hot flashes and night sweats; however, the exact mechanisms remain uncertain.

The study only included women not using hormonal contraception and those without hormonal disorders like PMOS (previously known as PCOS), leaving the impact of these variables on long-term body temperature yet to be determined.

Additional studies suggest that post-menopause, women’s body temperatures tend to normalize to levels similar to men.

Gombert-Labedens mentions that this midlife temperature increase may explain why many women in this age group report feeling less cold than they did earlier in life. “We hypothesize that the elevated body temperatures of middle-aged women may affect their environmental temperature perception,” she elaborates.

As smart rings and other temperature-sensing wearables gain popularity, it’s possible to pinpoint patterns and deviations in temperature trends that signal impending menopause, assess biological aging rates, and identify early signs of ovarian cancer and other conditions, according to Gombert-Labedens.