Way before we turned to Megaformers and Theraguns in an attempt to achieve wellbeing, cultures around the world relied on far more simplistic measures to keep them feeling good—things like heat and cold, for instance. Sweating it out in saunas and dipping into ice baths are just two of the long-standing practices that endure today, thanks to their resulting physical, emotional, and spiritual benefits. “Temperature has always been used a therapy,” says Elizabeth Gazda, CEO of wearable tech company Embr Labs. “The human body is built to absorb those therapies and use temperature stimulation for wellbeing.” So perhaps it’s not surprising that, in an everything-old-is-new-again twist, thermal manipulation is once again a hot topic in the wellness space—this time with modern scientific research and leading-edge technology driving the trend.

In general, our bodies stay within a tight core temperature range as we go about our days. “The body does try to stay at the same temperature—around 98.6℉—but it will cycle between a normal range of 97 to 99℉ depending on what may be going on, such as digesting food or entering the ovulation cycle in women,” says One Medical provider Michael Richardson, MD. (Actually, a recent study shows that the average body temperature is now closer to 97.5℉, which could be due to a decrease in infectious diseases since the Civil War era, when the 98.6℉ benchmark was established.) Strategic exposure to higher and lower temperatures, however, is thought to impact the body in ways that ultimately optimize its natural processes, from muscle recovery to sleep and stress relief.

Going to (temperature) extremes in the name of good health

Some of today’s most popular thermal therapies subject the body to extreme temperature exposure, creating stress and resulting in a desired physical effect. Cryotherapy, which involves spending three minutes in a chamber that’s hundreds of degrees below zero, is one of them. “It causes a tremendous amount of constriction in your blood vessels, and then you get a tremendous amount of dilation,” said Chill Space founder Josh Kantor, DC, in an appearance on Well+Good’s YouTube show What the Wellness. “The cold stress response, called hormesis, is a positive stress response that helps to reduce inflammation, reduce pain,  [and] improve muscle recovery. Athletes use it to get double training sessions in a day.”

Saunas, including the trendy infrared variety, have the opposite effect. They create a heat stress response similar to exercise, but magnified—heart rate increases, blood rushes to the skin, and sweat starts flowing in an effort to cool down the body. Uncomfortable as saunas may be, they’re thought to have many benefits. One study found that men who went to a sauna two to three times a week over 22 years had a 24 percent lower risk of high blood pressure, while those who went four to seven times a week saw their risk drop by 50 percent. Another small study found that infrared sauna use is correlated with alleviation of chronic fatigue syndrome symptoms and anxiety, while yet another indicated that infrared saunas may help people recover faster from workouts.

Here’s the thing, however: While extreme cold and hot therapies have been used for centuries, from Finland to China, there’s still more research to be done to confirm their actual impact. “There have been a number of health trends around using temperature regulation as a way to boost vitality, but the evidence for them is not always strong,” says Dr. Richardson. “Supporters of whole body cryotherapy, for example, promote its ability to help with pain and inflammation, but the research does not support these health claims in finding any meaningful benefit.”

The next generation of thermal wellness tech

Meanwhile, a new wave of thermal wellness tools is showing promising results by using more subtle forms of temperature manipulation, particularly where sleep is concerned. Temperature and sleep quality are closely linked, after all—when a person is falling asleep, skin temperature naturally rises while core temperature decreases, and the reverse is true for waking. Any disruption in this temperature shift can lead to a disruption in sleep patterns.

Sleep fitness and tech company Eight Sleep is seeking to address this problem with its newest bed, The Pod. “The number-one issue people have with sleep is temperature,” says Tomi Talabi, the brand’s communications director. “Foam and spring mattresses hold on to heat. So while your body is trying to lose the heat and cool down, your mattress, for the most part, is retaining this heat.” The Pod mattress solves for this with an internal matrix that uses water to dynamically heat and cool the bed’s surface in response to the user’s body temperature. It’s connected to an app that tracks its owner’s sleep stats and determines at which temperature they sleep the best. “We can even measure from our data how your workout is affecting your sleep—for instance, if you’re sleeping deeper if you did yoga at night,” says Talabi.

User data from the Pod seems to back up the idea that optimizing bed temperature leads to better zzzs. According to Talabi, after 30 days of using the Pod, users fall asleep 15 percent faster, toss and turn 10 percent less than normal, and experience up to a 17 percent increase in deep sleep. “You aren’t waking up constantly,” she says. “Sleep continuity is important for waking up feeling well rested and restored.”

The Embr Wave is another new thermal tool that’s helping people sleep more soundly at night.  The wearable device creates cool and warm sensations on the wrist, stimulating thermoreceptors that change the brain’s perception of the room temperature up to five degrees in either direction. Its companion app includes a program designed specifically for sleep, and it’s proving to be especially effective for menopause-age women who experience hot flashes and insomnia at night. A small study of 39 women with these symptoms found that wearing the Embr Wave helped them fall asleep 28 percent faster, while 28 percent fewer women studied met the criteria for moderate to severe insomnia while using the device.

Good sleep isn’t the Embr Wave’s only benefit. It was initially designed by three MIT students to counteract the frigid temperatures in their university lab space—a pain shared by anyone who feels like they always run hotter or colder than those around them. “If you’re in a controlled environment with more than a couple people, you could end up being the odd one out,” says Gazda, who notes that women tend to have more temperature-related challenges than men because of their hormone fluctuations. “Any time you’re uncomfortable, it’s a source of stress and distraction and lack of focus. It can push into your ability to enjoy yourself in the moment.”

To that end, Embr Labs is currently partnering with a variety of research organizations to learn more about the links between temperature and various health conditions, including anxiety, chronic pain, motion sickness, and obesity. Existing research has already established a possible link between social emotions and thermal sensations—a 2008 study showed that people drinking hot coffee perceived those around them to be more generous, trustworthy, and caring than those drinking iced coffee—and anecdotally, Embr Wave users are already claiming that the device is helping them manage social anxiety and stress.

So is thermal wellness worth paying attention to?

From a straightforward health perspective, Dr. Richardson says that if your body temperature is within a normal range, you don’t need to change it in any way. But that doesn’t mean you shouldn’t turn to thermal wellness if it makes you feel better. “If you find saunas really enjoyable and are using them safely, then it’s fine to keep using them, even if they’re not having any profound impact on your blood pressure or weight,” he says. “Quality of life is an important factor to take into account when deciding whether to use one of the latest wellness modalities, while you also consider its safety and efficacy.”  That said, if you’re pregnant or suffer from a serious health issue like heart or lung disease, he doesn’t recommend putting extra stress on your body by subjecting it to extreme temperatures. It goes without saying that you should talk to your doctor anytime you want to add anything new to your wellness routine.

It’s also worth mentioning that the current array of thermal wellness tools isn’t super affordable. The Embr Wave bracelet is $299, 8 Sleep’s Pod mattress starts at $2,295, and a single cryotherapy session can cost up to $100 in some parts of the country. But as with most technologies, as the demand rises the prices will hopefully fall—infrared sauna sessions now cost about as much as a boutique fitness class in many cities—and those who have experienced the benefits of these tools swear they’re worth every penny. “We’re in a new era of harnessing the body’s own pharmacy to feel better,” says Gazda. “That’s what we want to encourage our customers to do: Use your body’s own regulatory system for a sense of wellbeing.”

Wearables have come a long way lately—and your favorites are only going to get more advanced in 2020. On the low-tech temperature tip, did you know ice cubes can heat up your sex life?