Imagine you’re sitting in a quiet room with your eyes closed. Your breathing is slow and even. Your muscles are relaxed. Sunlight filters in through a nearby window, warming the air around you. All is serene. But then, without warning, the shriek of a nearby siren or the blast of a car horn shatters the silence. For decades, scientists (and horror-movie sound editors) have known that few things are as agitating as a loud and unexpected noise. Research on animals has shown that exposure to noise reliably activates the brain’s stress pathways and triggers the release of related hormones, such as cortisol. The World Health Organization has called noise pollution “one of the most important environmental risks to health” and a promoter of heart disease, mental health disorders, and other stress-associated conditions. But if certain sounds have the ability to unsettle and even sicken, it makes sense that other sounds would have the power to soothe. And there’s evidence that sound baths, better known as sound meditation, and other sound-based health practices may be uniquely therapeutic. “Sound — and in particular sound healing meditations using Tibetan singing bowls, gongs, and quartz crystal singing bowls — can be extremely calming,” says Tamara Goldsby, a research psychologist at the University of California, San Diego. For a 2017 study published in the Journal of Evidence-Based Complementary and Alternative Medicine, Goldsby and colleagues asked 62 men and women to undertake a one-hour sound bath. This involved lying on a yoga mat and listening to sounds made by a combination of Tibetan and crystal singing bowls, gongs, didgeridoos, and other instruments. No formal meditation was required; the people in the study were allowed to let their minds wander and were told it was okay if they fell asleep. Before and after the sound meditation session, the study participants completed questionnaires designed to measure their levels of tension, anger, anxiety, depression, pain, and other aspects of physical and emotional well-being. Following the hour-long session, each of these measurables had improved significantly, but sound meditation was particularly effective at countering tension, pain, anger, and confusion. Goldsby says sound meditation seems to work in part by switching off the body’s fight-or-flight stress responses — the same ones that are activated by loud or unpredictable noises. “Sound healing counters this [stress] response by invoking the parasympathetic nervous system, which slows heart rate, reduces blood pressure, and activates healing in the body,” she explains. On top of sound’s ability to induce relaxation and counter stress, Goldsby says there’s speculation that certain sounds — in particular, binaural beats created by playing two different sound frequencies at the same time — may actually shift brain activity into beneficial brain wave states. Just as sounds oscillate at different frequencies, which are measured in hertz, so too does the brain’s electrical activity. And there’s evidence that listening to specific binaural tones may adjust the brain’s electrical activity in ways that reduce anxiety and pain while promoting memory and attention improvements. ‘Sound healing counters this [stress] response by invoking the parasympathetic nervous system, which slows heart rate, reduces blood pressure, and activates healing in the body.’ Goldsby’s study did not include a control group and therefore didn’t rule out other explanations for the effects she and her colleagues observed. (For example, it’s possible that simply lying on a mat for an hour may reduce tension, pain, etc.) But there’s more research to suggest that certain sounds and the vibrations they create may have calming or otherwise therapeutic properties. One 2015 study in the journal Pain Research and Management found that five weeks of low-frequency sound simulation — basically, a combination of precisely calibrated sounds and vibrations — significantly improved sleep and reduced pain in 19 people with fibromyalgia. “When you present the ears with a completely regular pulse, you will see an increase in the number of neurons firing at that rate,” says Lee Bartel, co-author of that study and a professor emeritus at the University of Toronto’s Faculty of Music and Rehabilitation Sciences Institute. Put another way, exposing the brain to certain sounds or vibratory frequencies seems to coax it toward similar states of activity. Bartel says different brain wave states are associated with different patterns of cognition or wakefulness. For example, delta activity in the range of one to four hertz is associated with sleep, theta activity in the range of four to seven hertz is associated with relaxation and creative thinking, and beta activity in the range of 12 to 20 hertz is associated with complex problem-solving and concentration. By driving the brain toward these different states, Bartel says it’s possible that certain sound-based therapies can improve sleep, combat anxiety, sharpen focus, or produce other benefits. There’s also evidence that sound- or vibration-based treatments may change the activity of specialized cells in ways that improve blood flow or bone health. All of this is promising, but Bartel says the research to date is lacking — and that’s especially true when it comes to singing bowls and other “exotic” forms of sound therapy. “When you look through the many claims and theories advanced on the internet under ‘sound healing,’ many get into the zone of New Age quackery with no real scientific basis,” he says. While he and other researchers are working to firm up the science of vibroacoustic therapy, the studies to date on sound meditation and other forms of sound healing suggest that popular practices — including the sound baths that are now commonplace at yoga studios across the United States — are, at the very least, safe and may potentially hold real therapeutic value. “Sound is a very personal phenomena, and different individuals may resonate with particular types of sound healings,” UCSD’s Goldsby says. “Try out various types of sound healings and see what feels best.”