If you visit a flotation therapy center, you’ll put in earplugs and step into a rounded, podlike tub big enough for a tall person to lie back and stretch out. Depending on the center’s policies, you may be wearing close-fitting swimwear, or choose to wear nothing. In most cases you’ll close the pod door and lie back in quiet darkness, floating in water warmed to your skin’s temperature, about 95 degrees Fahrenheit. Or if you’re claustrophobic, you might be in an open tub. The water is about 10–12 inches deep and super-saturated with Epsom salts, or magnesium sulfate, so you’ll remain suspended effortlessly, hearing and feeling nothing.
Not all sensory input is shut off, however. For example, you could still create your own noise, of course, by vocalizing if you want. But the point of using a sensory deprivation tank is to muffle all sensations.
When you drastically reduce all inputs to your senses, a strange thing happens. Some people worry that sensory deprivation would induce anxiety. Instead, researchers have found that, for most healthy people, minimizing external stimuli such as light, sound, touch, smell, and taste, can have quite the opposite effect. A 2024 study of the effects of sensory deprivation tanks showed that immersing yourself in their womb-like atmosphere can dissolve your very sense of physical self and send your mind into an altered state of consciousness.
The researchers observed that due to the closely matching temperatures of the ambient air and subjects’ skin, the sensory deprivation setup “appears to blur the boundaries between air, body, and water,” they wrote in their paper, published in the journal Scientific Reports. “This blurring of boundaries leads to an [altered state of consciousness] where one can no longer discern where their body begins and ends, the essence of body dissolution,” the researchers wrote in the journal Scientific Reports.
Flotation tanks, as they are also called, are a growing business in the U.S., with hundreds of float therapy centers opening since their commercial use began in the early 1970s. American neuroscientist and psychoanalyst Dr. John.C.Lilly invented the first sensory deprivation tank in 1950 while working at the National Institute of Mental Health. Fascinated by the nature of consciousness, he designed a system that would ideally allow him to observe his own mental state with no environmental distractions. While his original design began with complete submersion and the need for a breathing mask, over the years he developed a more user-friendly flotation tank. It’s had the same basic design for about 50 years. Since around 2000, public interest has taken off as an alternative wellness therapy, possibly due partly to more celebrity endorsements—comedian and UFC commentator Joe Rogan touts their benefits, for example. The Isolation Tank Market Industry is worth $3.7 billion this year, and will likely grow to $10 billion by 2034, according to global market research company Market Research Future.
san francisco giants pitcher hunter strickland uses the salt water sensory deprivation tank monday, feb. 28, 2017, inside the new sports science room at scottsdale stadium in scottsdale, az. (karl mondon/bay area news group)
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San Francisco Giants pitcher Hunter Strickland uses the salt water sensory deprivation tank in 2017 inside the sports science room at Scottsdale Stadium in Scottsdale, Arizona. Athletes and celebrities have been publicizing the benefits of float therapy for years.
Depending on the therapy center, a session can last between one and three hours, fostering a sense of profound inner calm by removing distractions such as ambient noises, light, smells—and even the sensation of gravity. Perhaps it’s the closest you can get to floating in space.
As a result, users of flotation tanks can shift into altered states of consciousness, in which the brain experiences a dream-like state without actually being asleep. People who entered these altered states reported in the Scientific Reports study that they also couldn’t tell how much time had passed once the session was over and they emerged from the tank. And users also experienced a lack of normal bodily sensation of any kind—in other words, it seemed like they had no body.
The study placed 25 men and 25 women in two different sensory deprivation settings to compare their effects: one hour in a float tank and one hour in a warm waterbed in a dark and quiet room. Beyond the general calming and anxiety-relieving feeling of lying back on a waterbed, people in the flotation tanks also felt that the lines between their bodies and their surroundings had blurred to the point of becoming indistinguishable. They also reported losing an accurate sense of the passage of time. These altered states of consciousness relieved floating participants of anxiety and stress to a far greater degree than for those on the beds, the researchers wrote, and participants felt more relaxed after floating.
One of the study authors, clinical neuropsychologist Dr. Justin Feinstein of the Laureate Institute for Brain Research, talked about what happens to your brain during a presentation at the 2018 Float Conference in Portland, Oregon, where the world’s science and industry experts on float therapy gather annually. He said that, “if you’re in a well-calibrated flotation tank, not a single photon of light should be entering your brain, which means the entire posterior sector of the brain that’s responsible for processing and creating our visual world suddenly doesn’t have information coming in.” The same is happening for the part of your brain that registers sounds—no sound is forthcoming in the flotation tank. Likewise, when the temperature of the air, the water, and your skin is perfectly calibrated, you really do lose tactile sensation completely, Feinstein explained.
A 2021 study published in the journal Human Brain Mapping and also led by Feinstein, scanned the brains of 24 healthy volunteers just before and after multiple float therapy sessions of 90 minutes each. A separate group simply reclined in a memory foam chair in a dark room for an equal amount of time. fMRI results showed that the different regions of their brains communicated less with each other after sessions in both types of activities. However, the floating session led to a particular quieting of the brain’s default mode network, a network of connected brain areas that are more active while daydreaming, producing a sort of inner dialogue. In a way, the session emptied their minds.
Feinstein’s research on flotation therapy has also found that the heart rate, blood pressure, and breathing rate all slow significantly as well during a float session.
However, at least one piece of research has found a less typical and potentially concerning reaction in people experiencing total sensory deprivation. Participants in a 2015 study were placed in a completely darkened, completely silent anechoic chamber—not a float tank—for up to 25 minutes. Some of them hallucinated while in the chamber, though researchers wrote in the journal BioMed Research International that this result was more likely for people who were already prone to hallucinations because of underlying mental health issues. Neuroscientists have found that in some cases, prolonged sensory deprivation can cause the visual cortex to create its own imagery.
Floating seems to be a comforting contrast to an anechoic chamber, but research like the 2015 study indicates that it may not be for everybody. For healthy people who get an okay from their doctor, float therapy could be “a profound intervention for the nervous system” that is otherwise being constantly inundated with information, Feinstein said. It’s a deep inner stillness that comes with practiced meditation, but in a sensory deprivation tank, all you have to do is lie back and close your eyes. It’s the ultimate form of disconnecting from the world and your own mental chatter.
Want to try float therapy? You can visit Flotation Locations at https://floatationlocations.com/ Before you dive in though, you should ask your doctor if float therapy is safe for you.
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Before joining Popular Mechanics, Manasee Wagh worked as a newspaper reporter, a science journalist, a tech writer, and a computer engineer. She’s always looking for ways to combine the three greatest joys in her life: science, travel, and food.