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Without knowing it, you are being exposed to dangerous levels of airborne ultrasound, according to a new study by University of Southampton researchers. In places such as railway stations, museums and libraries, the levels of these sounds are high enough to make people complain about "nausea, dizziness, fatigue and other negative effects", which could actually be sourced from places such as door sensors and public address systems.

A number of employees who have been exposed to ultrasound due to the nearness to industrial devices have also spoken about similar negative effects, but there is not enough information or research to prove the link between the two variables.

Still, Tim Leighton, a team member of the current research, feels that the existing guidelines are inadequate to safeguard safety levels.

"Existing guidelines are insufficient for such large public exposures as the vast majority refer to occupational exposure, where workers are aware of the exposure, can be monitored and can wear protection," Leighton said in a press release. "Furthermore, the guidelines are based on the average response of small group, often of adult males."

"The guidelines are also based on an insufficient evidence base, most of which was collected over 40 years ago by researchers who considered it insufficient to finalize guidelines, but which produced preliminary guidelines," he added.

With the help of smart phones and tablets, along with with an app, Leighton and his team found that they could produce a spectrogram of what they had with their microphones. This led to the discovery of very high frequency/ultrasonic fields (VHF/US) at various public buildings that had hundreds of people during the time of the study.

The public was exposed to high levels that crossed 20 kHz, known as the "safety threshold" according to the current guidelines.

"Individuals who are unlikely to be aware of such exposures are complaining, for themselves and their children, of a number of negative conditions," he said. "The lack of research means that it is not possible to prove or disprove the public health risk or discomfort. However, it is important that sufferers are able to identify the true cause of their symptoms, whether they result from VHF/US exposure or not."

The study will be published in the Proceedings of the Royal Society.