A mysterious force lurking in old buildings, basements and even ventilation systems may be quietly affecting people's emotions, but is often misunderstood as "haunting" or a strange atmosphere. The latest research points out that this power is not a supernatural phenomenon, but a low-frequency sound that the human ear usually cannot consciously hear - infrasound. It can silently change people's mood and increase the level of the stress hormone cortisol in the body.
Infrasound refers to sound waves with a frequency lower than 20 Hz. This frequency band is usually beyond the range of human hearing, but it is widely present in daily environments. It can come from natural phenomena such as storms, or from man-made sound sources such as traffic and industrial equipment. Some animals even use infrasound to communicate over long distances, while other animals will actively avoid such low-frequency vibrations. In a new experiment, the research team found that even if humans are not aware of the presence of these sounds, the body will respond, manifested by increased irritability and elevated salivary cortisol levels.
One of the corresponding authors of the paper, Professor Rodney Schmalz of MacEwan University in Canada, pointed out that infrasound is “almost everywhere” in the real environment, from ventilation systems to traffic noise to various industrial machinery, and people are often exposed to it without knowing it. He said that experimental results show that even short-term exposure may quietly change mood and stress hormone levels, which reminds us that it is necessary to face up to the impact of infrasound in real environments and re-examine some experiences that have been given a "supernatural color".
In his opinion, the inexplicable nervousness and uneasiness that one feels when walking into a "haunted building" is probably related to infrasound rather than the so-called ghosts. In old buildings, especially underground spaces, aging pipes and ventilation systems often produce low-frequency vibrations, which are combined with factors such as dim environment and closed space, which can easily cause psychological implications. Once people are preconceptionally told that "this place is haunted," it is easier for people to attribute such physiological and emotional changes to supernatural phenomena, while ignoring the underlying physical causes.
To verify the specific impact of infrasound on humans, the research team recruited 36 volunteers and arranged them alone in a room to listen to music designed to have soothing or disturbing emotional colors. During this process, only half of the subjects were unknowingly exposed to the 18 Hz infrasound environment produced by a hidden subwoofer. After listening to the sound, all subjects were asked to describe their current feelings, evaluate the mood of the music, and answer whether they thought infrasound existed in the experiment. They also provided saliva samples before and after the experiment to detect cortisol levels.
The results showed that participants who were exposed to infrasound during the experiment had significantly higher salivary cortisol levels and were more likely to subjectively report feeling irritable, less interested, and rate the music as sadder. It is worth noting that even with these objective and subjective changes, most subjects were still unable to accurately judge whether infrasound was played in the experiment, which means that the body's response to infrasound is not consistent with the individual's explicit perception and subjective beliefs.
Schmalz said the study suggests the human body can respond to infrasound "inaudibly." The experimental data showed that there was no detectable correlation between participants' judgments about the presence of infrasound and their mood and cortisol levels, suggesting that perceptions and cues were not dominant factors in this experiment. The first author of the study, Kyle Scatetti, a doctoral student at the University of Alberta, further pointed out that irritability and elevated cortisol are naturally linked, but the additional effect of infrasound exposure on both indicates that this low-frequency sound itself is an independent and worthy of attention.
At present, the scientific community has not fully understood the mechanism through which humans respond to infrasound at the unconscious level. This issue still needs further research at the physiological and neurological levels. However, this work has raised practical concerns about whether long-term exposure to infrasound in daily life or work settings may lead to adverse health consequences due to persistently high levels of cortisol, including mood problems, irritability, and a decrease in overall well-being.
Study co-author Professor Trevor Hamilton of MacEwan University pointed out that cortisol helps the body cope with stress in the short term and keeps people highly alert. This is an adaptive mechanism formed during the evolution process. However, he emphasized that long-term or repeated high cortisol exposure will bring about a series of physiological problems and may change mental health conditions. This is also one of the long-term concerns in the field of noise and public health research.
Due to the limited sample size of this study, the research team conducted a sensitivity analysis before drawing conclusions to confirm that the experimental design had at least the statistical power to detect gold medium and above effect sizes. The analysis results support the reliability of the main findings, but the researchers also admitted that to fully understand the impact of infrasound on human emotions and behavior, further verification in larger and more diverse samples is needed, and more objective indicators are introduced.
Scatetti reminded that this is a "beginning research" to explore the impact of infrasound on humans. Currently, only a single frequency condition has been tested, while infrasound in real environments is often composed of multiple frequencies superimposed. Different frequencies and combinations may have different effects on emotions and physiology. Future research needs to systematically draw this "frequency-effect map", and at the same time record and analyze the subjects' behavioral and physiological responses in real time during the experiment, rather than relying solely on subjective self-reports afterwards.
Schmalz said that the next priority task is to conduct tests in a wider frequency range and longer exposure time to get closer to the complex and changing environmental infrasound conditions in reality. He believes that once the rules of the emotional and physiological effects of different frequency bands and their combinations are clearer, these findings are expected to be incorporated into noise regulatory policies or building design standards, such as more scientific acoustic isolation between underground spaces, industrial facilities and residential areas.
As a scholar who has long studied pseudoscience and misinformation, Schmalz specifically pointed out that the "scary thing" about infrasound is precisely that it can trigger real and measurable physiological and psychological reactions even though it is invisible and inaudible. He suggested that when people face the inexplicable "weird feeling" in the basement or old building, they might as well first think of the low-frequency vibrations emitted by pipes and equipment instead of rushing to blame the cause on "wandering souls."
According to reports, this study is titled "Associations between Human Infrasound Exposure and Aversive Responses, Negative Evaluations, and Elevated Salivary Cortisol" and was published in the journal "Frontiers of Behavioral Neuroscience" in March 2026. It was co-signed by Scatetti and others. The project received funding from the Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Fund.