The Silent Stress: How Sounds You Can’t Hear Might Be Messing with Your Mood
Featured paper: Infrasound exposure is linked to aversive responding, negative appraisal, and elevated salivary cortisol in humans
Disclaimer: This content was generated by NotebookLM and has been reviewed for accuracy by Dr. Tram.
Have you ever walked into a room and suddenly felt a sense of unease, even though everything looked normal? Or perhaps you’ve visited a “haunted” location and felt a strange chill or a feeling of being watched? While many people point to ghosts or “bad vibes,” science suggests there might be a much more physical—and invisible—culprit at work: infrasound.
A recent study published in Frontiers in Behavioral Neuroscience by researchers at MacEwan University has shed new light on how these low-frequency sounds impact our bodies and our emotions. The most surprising part? Even when you can’t hear the sound, your body is still listening.
What is Infrasound?
To understand this, we first need to talk about the limits of human hearing. Most humans can hear sounds in the range of 20 Hz to 20,000 Hz. Infrasound refers to sound waves with a frequency below 20 Hz, which is generally too low for the human ear to pick up as a distinct sound.
Even though it’s silent to us, infrasound is everywhere. It occurs naturally during volcanic eruptions, tectonic activity (earthquakes), and massive storms. But in our modern world, it’s also a form of human-made “pollution.” You can find infrasound humming away in urban areas near air conditioning units, ventilation systems, heavy traffic, and even wind turbines.
The Experiment: Music, Saliva, and Silent Subwoofers
Researchers wanted to know if this silent hum could actually change how a person feels. To test this, they brought 36 university students into a controlled lab environment. The setup was clever: participants listened to either “calming” or “unsettling” music for about five minutes.
While the music played, the researchers used powerful, out-of-sight subwoofers to blast 18 Hz infrasound at a steady volume (75–78 dB) for some of the participants. Others listened to the music with no infrasound at all.
To see what was happening inside the participants’ bodies, the researchers didn’t just ask them how they felt. They collected saliva samples before and after the music to measure levels of cortisol, a hormone that the body releases when it is under stress.
The Results: A Body Under Stress
The findings were striking. Even though the infrasound was “silent,” it left a clear mark on the participants’ physiology and mood:
- The Stress Hormone Spike: Participants exposed to the infrasound had significantly higher levels of cortisol in their saliva after the experiment compared to those who didn’t experience the low-frequency waves. This suggests that the body treats infrasound as a stressor, triggering a biological “fight or flight” type of response.
- Increased Irritability: On mood surveys, people in the infrasound group reported feeling more irritable while listening to the music. It didn’t matter if the music was supposed to be calming or scary; the infrasound made them more annoyed regardless.
- Loss of Interest: The “silent” sound also acted as a buzzkill. Participants reported feeling less interested in the music and described the music itself as less interesting when the infrasound was turned on.
- A Sadder Perspective: Perhaps most interestingly, when the infrasound was on, people were much more likely to describe the music as “sad”. It seems the sound waves were actually tinting their emotional perception of the world around them.
The “Ghost” in the Room
One of the most important parts of this study was whether the participants actually knew what was happening. If they could hear the low rumble of the subwoofers, they might just be getting annoyed by the noise.
However, the researchers found that participants were no better than chance at guessing whether the infrasound was on or off. Essentially, they couldn’t hear it, but their bodies were reacting anyway. This rules out the “placebo effect”—they weren’t just acting stressed because they thought a weird sound was playing; their bodies were reacting to a stimulus they weren’t even consciously aware of.
This might explain why some “haunted” houses have such a bad reputation. Older buildings with rumbling pipes or vibrating fans might be creating pockets of infrasound. A person walking into that room wouldn’t hear a thing, but their brain might register a spike in cortisol and a feeling of irritability or “creepiness,” leading them to believe the room is haunted.
Why This Matters for You
We live in a world that is getting noisier, but we often only think about the noise we can hear. This study suggests that infrasound is a hidden environmental irritant.
If you live near a busy highway, work in an office with a massive, vibrating HVAC system, or live near industrial machinery, you might be bathing in infrasound all day. Over time, this could lead to unexplained stress, a shorter temper, or a general lack of interest in things you usually enjoy.
The researchers point out that while we’ve known for a while that animals like fish and mammals react to infrasound, we are only just beginning to understand the “non-auditory” ways humans perceive sound. It’s possible that our ears aren’t the only things “hearing”—our vestibular system (the part of the inner ear responsible for balance) might be picking up these vibrations and sending stress signals directly to the brain.
The Takeaway
The next time you feel inexplicably annoyed or stressed in a certain building or area, take a look around. Is there a large fan humming? Is there heavy traffic nearby? You might be experiencing the physiological impact of sub-audible infrasound.
As we continue to build bigger machines and more complex cities, understanding this “silent” pollution becomes vital. Science is proving that just because a sound is out of earshot doesn’t mean it’s out of mind—or out of our bodies.