“Noise has boundaries. Silence has none.” - Meeta Ahluwalia
We live in a world that is teaming with sound, all the time, 24 hours a day. From our oceans to the soil beneath our feet, every inch of the world and every corner of nature generates its own unique symphony of sounds--humming, screeching, crinkling, popping, roaring, barking, chirping—all of which make up a rich cacophony of communication and interaction. Even planet Earth emits its own unique soundscape, a frequency that is broadcast to the vast universe. Sound is everywhere; it seems to be part of the very essence of life.
Luckily, many sounds have frequencies that cannot be detected by the human ear, which keeps all the ruckus of our world at manageable levels. Even though the natural world is teeming with sound, humans have done more to change the soundscape of Earth than any other species. We build machines that, for better or worse, emit lots of sounds, and by doing so have turned up the volume of life. There are many consequences to human engineering; the noise it creates impacts our own health as well as that of the planet. Unlike other species that emit sounds as a means of communication, the rumbles, pings, and buzzing of human invention range from those that blend into the background, like the hum of a refrigerator, to those that negatively impact the health of many species, such as the vibrations of cruise ships. Tolerance of sound is incredibly variable within nature; just within humans we find vastly different sensitivities to frequencies, volumes, and tonality. One person’s joyful music is another’s disturbance of the peace.
Even though there is a good deal of difference in our tolerance to certain sounds, we can still find common ground in those we find pleasant and those that are disturbing or intolerable. Many enjoy the sound of a gentle breeze or ocean waves, whereas the screech of fingernails on a chalkboard makes us cringe. As a rule, when sounds are experienced as unwanted, unpleasant, or loud they shift into a category we refer to as noise. Still, what we consider noise is quite subjective, especially for sounds that are measured at or below 60 decibels (dB). In the past decade, research on the effects of noise shows that sounds at 70 to 80 dB are not a matter of individual preference but a public health concern, as noise at these levels directly impacts our physiology and can even be deadly.
For years, concern about the effect of noise on our health was the work of organizations involved in occupational health. But in the past decade, the medical community has jumped into the arena, establishing clearer guidelines for safe noise levels that go beyond the workplace. Through this research, we are gaining a clearer understanding of how different intensities of everyday sounds, measured in decibels, impact our health. For context, a normal conversation between two people is typically 60 decibels (dB), whereas gas-powered cars measure in at about 70 dB. Traffic noise bumps up to 90 dB when trucks are added to the mix, which is why traffic is identified as a major environmental stressor, second only to air pollution. Combine that with the typical sounds that make up our modern urban landscape--sirens, airplanes, above ground subways, jackhammers, and construction equipment--and noise levels can easily reach or exceed a whopping 120 dB.
We’ve long known that chronic exposure to loud noise is linked to hearing loss, but research shows that the effects of chronic exposure to unhealthy levels of noise can be insidious. With consistent exposure, most people’s auditory systems accommodate to the chronic din of an urban landscape, even when noise reaches unhealthy levels of 70 dB or above. Lack of awareness, however, does not mean noise isn’t causing harm. Evidence of the physiological effects of unhealthy noise can be measured equally in the cells and organs of those who dislike the noise, as well as those who seem unaffected. This is why the medical community designates unhealthy noise levels at or above 70dB as, somewhat ironically, a “silent killer”.
Although a human cannot hear with the same sensitivity as some other animals, hearing is an important sensory function that is viscerally connected to our feelings of safety. Our auditory system is always scanning our environment for threats; this happens even when we aren’t paying attention. When sound reaches the brain, it stimulates both the auditory cortex, which interprets the noise, and the amygdala, which triggers our emotional response to it. Certain sounds, especially those with low frequencies such as a rumbling or growling, are more likely to trigger our nervous system into overdrive. Our nervous systems like predictability, so we are also sensitive to sudden spikes in loudness or changes in tonality, both of which can be interpreted by the amygdala as a threat. It is one of nature’s brilliant ways of keeping us safe—it keeps us ready to run from a threat even before we are fully aware of the danger.
Once the stress response is initiated, the body releases adrenaline and cortisol, which impacts the functioning of our arteries and blood vessels, making some dilate and others constrict. Our blood pressure increases as does the release of glycogen and fats into the bloodstream, providing quick fuel for our muscles in anticipation of fighting or running away from danger. But because our modern-day stressors don’t involve battling a grizzly or running from a lion, the escalated hormones, sugar, and fats continue to circulate in the bloodstream, causing oxidative stress and inflammation in the lining of blood vessels. Herein lies the primary damage that noise inflicts on our physiology: it seems to specifically target the inner lining of the arteries and blood vessels, contributing to a range of cardiovascular dysfunction, from high blood pressure to plaque buildup, as well as obesity and diabetes.
Exposure to unhealthy noise levels can change us on a deep, cellular level, impairing the functioning of our endothelium, the tissue that forms a single layer of cells that line our blood vessels. And whereas researchers assumed that the negative effects of noise pollution are cumulative, developing after years of exposure, studies of healthy young adults who were exposed to recordings of trains while they slept showed marked signs of changes in blood vessels after just one night of exposure.
Anyone who chooses to live in an urban setting, such as Manhattan, will most likely stop noticing the constant din of urban life once they have settled into their environment. Although we can habituate to noise, it does not mean that our health will not suffer. Unhealthy levels of noise at or above 70 dB will initiate a stress response even if the loudness doesn’t bother us. The clearest evidence of this phenomenon comes from studies that measure how loud noises impact people while they are sleeping. Whereas the rest of our senses downshift during sleep, our auditory system remains active, scanning for sounds in our environment that may indicate danger. Provided they occur somewhat frequently, we can become habituated to certain loud sounds that occur regularly while we sleep, such as train whistles, television, fire engines, even snoring. However, even though the noise does not wake us up, it still initiates a stress response which, with just limited exposure, can seriously compromise our cardiovascular system. What we think is a restful night’s sleep can be a stressful event if we have been exposed to unhealthy levels of noise throughout the night. The bottom line is that noisy environments do not need our awareness to be stressful; just exposure to noise at unhealthy levels can make us sick.
As data related to unhealthy levels of noise continues to accumulate, it is important to keep in mind that, as with all issues related to health, it can be hard to distinguish between causality and correlation. Our lives, as well as our physiology, are complicated and messy, which makes it hard to isolate all the variables in an environment that might trigger a stress response. Urban areas are busy places, so is it the noise that is stressful, air pollution, or some other variable? And scientists have yet to fully understand the distinction between decibel levels and the perception of noise; there is variance in the levels at which people show signs of stress. Even at 70 dB or greater, there are those who find louder noises to be comforting and soothing. Studies of hospital intensive care units find that some patients are comforted by the sounds of ringing phones, loud talking, and clattering instruments, experiencing less stress and faster recovery times in noisy environments.
Until we gather more data and get a clearer picture, we can keep in mind two key findings from what we know so far. First, noises at levels above 70dB can trigger a stress response, even if we don’t notice the sound. Secondly, we might get used to loud noises, but our bodies do not. Our auditory system interprets loud noises as a threat and triggers our bodies to respond accordingly. And what we are learning about noise points to a broader message, one that reminds us that there are a multitude of factors that impact our health; some are within our control while others are not. All we can do is the best we can with the resources we have while attending to our well-being with a generous dose of compassion.
This week, I invite you to spend a few minutes each day becoming familiar with the sounds around you. Tune into your own personal soundscape, noticing which sounds you find calming and appealing, as well as those you find irritating. What is your tolerance for loud noises and how do they change your behavior? What kinds of sounds keep you grounded, calm, and make you feel safe? Take some time to listen and notice how your body reacts. You may be surprised by what you do—or do not--hear.
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