Quiet hum of household appliances can be harmful to the kidneys

In the experiment, mice were exposed to noise for 12 hours a day over a period of five days — during the nighttime, when the animals are most active. The researchers recorded the actual noise from the outdoor unit of an air conditioner and a water heater, and then, using audio software, they separated it into two components: low‑frequency (up to 100 Hz) and high‑frequency (above 100 Hz). At the same time, the sound pressure level was the same in both cases, in order to check whether it is the frequency that matters, and not the volume.

To assess the condition of the kidneys, two standard biomarkers were used: the levels of creatinine and urea nitrogen in the blood. An increase in these levels indicates that the kidneys are less effective at filtering waste. It turned out that the full spectrum of noise increased both indicators, confirming kidney damage. The high‑frequency component had no effect. However, low‑frequency noise, even inaudible to mice, led to the same increase in markers as the full spectrum.

To understand what is happening inside the organ, the researchers studied the structure of the kidneys. They contain glomeruli — microscopic plexuses of blood vessels that act as filters. In mice exposed to low‑frequency noise, these structures were swollen, and the filtering membranes were thickened. This indicates a disruption in the normal functioning of the filtration system.

The key link in the damage mechanism turned out to be endothelin‑1 — a molecule that regulates vascular tone. Normally, it helps maintain the balance of blood flow, but under the influence of low‑frequency noise, its production increased, which led to the narrowing of renal vessels and a deterioration in tissue blood supply. To confirm this hypothesis, the scientists gave a second group of mice ambrisentan — a drug that blocks the action of endothelin. In these animals, kidney parameters remained closer to normal, and structural damage to the glomeruli was significantly less pronounced. According to the authors, the signaling pathway involving endothelin plays a central role in the negative effect of low‑frequency noise.

The study was conducted on mice, so these conclusions cannot yet be directly applied to humans. Nevertheless, the results indicate the need to take low‑frequency noise into account in future studies examining the impact of the environment on human health, as this component of noise is often ignored.

Interestingly, the same researchers previously found beneficial effects of low‑frequency sounds, such as reduced motion sickness and changes in blood flow in the skin’s blood vessels. This may suggest a dual nature of low‑frequency effects. Their biological impact depends on frequency, sound level, and duration of exposure. In the future, the team plans to study in detail under what conditions such sounds are harmful and under what conditions they can be beneficial.

The scientific work demonstrates that quiet low‑frequency noise from household appliances can be a potentially significant risk factor for kidney health. The decisive factor here is not the volume, but a specific frequency that can trigger adverse physiological reactions even without the involvement of auditory perception.